New Sub Forum needed - Astro scopes for Visual (1 Viewer)

camera Live View experiment

As far as using the camera Live View, it seems to work just fine. In fact, as I panned the gear head, the scene brightness changed and the camera's Live View adjusted the brightness level for me (it also adjusted automatically for the darker view with the polarizer attached!). Very nice views, just wish the screen was bigger!

Also, my camera Live View is not like a TV/video camera that senses right-side up and upside-down (rotating the camera does not change the upside-down image on the LCD screen). Maybe what I need is a very small video camera??

This is approximately at 30x magnification (~1500mm/50mm), so following some ducks on the water or shorebirds feeding should not be a problem. The only problem was the upside-down image, so I have to buy a t-adapter that can hold my Brandon 32mm eyepiece. That will be the next phase in the experiment.

Something very nice is the auto zoom function on the camera. Pressing the OK button zooms the image on the screen by 2x, 4x, 8x as needed. Very nice view and clear. Can see the heat waves deforming the image. Cool.

I might be able to zoom if I attach a small focal reducer to my Nikon zoom eyepiece, not sure how that might work. Might have to borrow a cheap used 1.25 inch focal reducer from one of my astronomy contacts. (No, just found out my zoom eyepiece is too big for the intended adapter - pays to measure things before buying!).

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camera live view update

Update: Live View when zoomed is not as sharp as the eyepiece by itself. Could see the ducks and gulls today better with the 32mm eyepiece (about 47x power) compared to the camera by itself (about 30x power digitally zoomed 2x to 60x power).

I hope to get a projection eyepiece adapter and see if Live View works better when the image is magnified by an eyepiece. Hopefully, will know more by next week.

3

web cam for birding

More silly possibilities! Would have to glue a 42mm step adapter ring to the outside housing, so not pursuing this yet.

http://www.bhphotovideo.com/c/product/893197-REG/Microsoft_q2f_00013_Lifecam_Studio_PL2.html

3

I'm not sure if you already had a look at:
http://www.pt-ducks.com/cr-telescopes.htm#Test%20of%20image%20erectors
http://www.pt-ducks.com/cr-telescopes.htm#Test%20of%2082%C2%BA,%20100%C2%BA%20and%20102%C2%BA%20AFOV%20zooms
http://www.pt-ducks.com/cr-telescopes.htm#CR-binoviewing

good comparison photos

DRodrigues said:

I'm not sure if you already had a look at:
http://www.pt-ducks.com/cr-telescopes.htm#Test%20of%20image%20erectors
http://www.pt-ducks.com/cr-telescopes.htm#Test%20of%2082%C2%BA,%20100%C2%BA%20and%20102%C2%BA%20AFOV%20zooms
http://www.pt-ducks.com/cr-telescopes.htm#CR-binoviewing

Click to expand...

Ahh yes! I had seen your web site one or two years ago and that is what gave me some ideas about using a mirror scope at that time. You have some great field equipment, especially for reading tags on legs of birds. Always good to repost the links so more people will discover it! You must keep it posted, it is a great reference for others to learn from.

I then bought a used Vixen 110L which is a nice "modified Cassegrain" but found it awkward at the time. If I had it now, I think I would have a better way of handling it. So, I still like the mirrors but trying to find a way to boost contrast. The latest idea is to use a web cam output to an ipad like device, but not ready to experiment yet. Have to prove that the eyepiece magnification works well first. Just got the projection adapter today from Agena Astro in california. I will report back my results in a few days.

B

natural colors and other discoveries

89mm Maksutov photo of Northern Pintail Duck

An example of prime focus photography (no eyepiece) with the 89mm maksutov. I think it is around 32x power (1600/50) at about 540 feet according to Google Earth. I like it. Took many blurry shots and a few sharp ones. The visual seeing is nice and sharp too. Finding that 89mm is too small to allow enough light in, I like *brighter* images as well as good contrast and more magnification (60x). The little scope is great to carry around, shorter than a refractor and lighter too. So, it has a definite place. And still have to get a web cam to experiment with a visual screen for a group of birders to look at.

But I still want MORE of the bird to see. Does that make sense?!?! It is a strange craving, I want a live view with my eyes but more detail and larger scale, like I am there with it. So, I am now thinking of complimenting my setup with a 6" SCT telescope. More light, can then safely use my circular polarizer without it becoming too dark. And shorter than a 4" refractor but with more inherent focal length for easy magnification with comfortable eyepieces (eye relief, pupil exit size, etc).

Something else that I am noticing about what I like - I like the natural colors that mirror scopes render compared to the "cool" or "warm" images that are seen through a refractor. And this dawned on me while I was viewing the birds this last time out. Of course, eyepieces also "color" an image too, so I have found that I like the more neutral orthoscopic type of eyepieces, so far anyway.


:eat:

6 inch SCT

More craziness. Sold off a couple of unused photo items and just put an order in for this 6 inch Meade SCT.
http://www.highpointscientific.com/meade-6-quot-sct-ota-with-uhtc-coatings-sctota06

Should get more magnification with brighter view of the bird. And a faster shutter speed with the camera. We shall see...
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I have the Celestron version, C6. I didn't like it for daytime use as much as I like the Maksutov design. It is easy to get a central obstruction image during daytime when your iris opening is lower than 2mm (with long focal lengths, my 31mm and even my 24mm if I remember right) and there's the field curvature, more brittle Schmidt lens in comparison with the Maksutov meniscus and need for colimation when used in hard conditions. A 4-6" MCT might work better and it is also generally sharper with less central obstruction. I know of Mak camera lenses but not of Schmidt ones outside astronomy.
But you'll see if it suits you.

CAT quirks

kkokkolis said:

I have the Celestron version, C6. I didn't like it for daytime use as much as I like the Maksutov design. It is easy to get a central obstruction image during daytime when your iris opening is lower than 2mm (with long focal lengths, my 31mm and even my 24mm if I remember right) and there's the field curvature, more brittle Schmidt lens in comparison with the Maksutov meniscus and need for colimation when used in hard conditions. A 4-6" MCT might work better and it is also generally sharper with less central obstruction. I know of Mak camera lenses but not of Schmidt ones outside astronomy.
But you'll see if it suits you.

Click to expand...

Thank you for your experience! I appreciate your input!! I already experience some small amount of central obstruction dimming with the Questar (a Maksutov) and the 32mm Brandon eyepiece that came with it. I expect some also with the larger SCT. Not sure how small my iris gets on bright days looking through a scope! Never thought of it but will be testing the scope this weekend and will try to look at things of wide brightness levels to get a sense of any effect upon central obstruction dimming. I might have to use higher power eyepieces like 25mm to avoid the issue.

(I also like the Maksutov design but the 6 inch versions are a little more than twice the price, longer, and slightly heavier).

The reference material I am basing my thoughts on are my own experience with the Maksutov and the old Better View Desired review of CAT scopes back in 1993 (revised 2007). Optical advances have occurred since then but the basics are still the same. I am hoping to see much larger scale and detail from the same eyepieces I already use. They state that the C5 tested gave "...more than twice the resolution of the best refractor that I have tested." More bird to see, I hope.

Also, I don't expect to use this scope for heavy field work. Just the special cases where the view is relatively static and not much walking needed. And I am used to collimation issues and I find it relatively easy (used to own a Vixen 110mm modified Cassegrain). We shall see!!

o

Meade LX80 test

Test of new Meade 6 inch Schmidt-Cassegrain Telescope. Eastern Bluebird was 30 feet from me and very accomodating. Standard post-processing applied.

Eastern Bluebird with Meade LX80, 6 inch

Views are brighter than the 89mm Questar, shutter speed with same type of connection is at least one stop faster (I think more). I forgot to bring my circular polarizer, so I will have to test again but I did put on my polarized sunglasses to simulate some polarization for VISUAL use. Very nice view, did not seem too dark and my eye adjusted somewhat to the dimmer light. Of course, this was full sunlight at about 4pm. Will have to see for the next test with the real polarizer. Even without the polarization, the visual use is very nice, does not look uncontrasty!

Strangely enough, many of the photos came out less contrasty than using it visually with an eyepiece. The central obstruction must subtract enough contrast for the camera sensor (APS-C type) to notice. The human eye maybe can adjust on-the-fly so-to-speak, so the visual use is very acceptable. And digital photos are adjustable for contrast and microcontrast. So, this may end up becoming a dual-use scope when I feel like carrying it around. It is 12 lbs. and was OK in a medium-sized backpack lined with hard foam. All pieces of the scope are metal except for the plastic front cap and mirrors inside.

Also, I did not bother collimating it, this is straight from the shipping box. Collimation might be off a little bit from what I could see but will have to do a real star-test.

More tests needed!
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There's a very large central obstruction on that scope. Meade gives no spec for it, but I saw a reference that gave the diameter as 2.76". That would be a 46% obstruction, which would drop the Strehl ratio to below 0.7 before aberrations are even considered. I doubt that a real world specimen would have a Strehl any better than 0.6, probably closer to 0.5. Whether such a scope has enough contrast for a "good" visual image would I guess depend on the viewers expectations.

view for the $$$

henry link said:

There's a very large central obstruction on that scope. Meade gives no spec for it, but I saw a reference that gave the diameter as 2.76". That would be a 46% obstruction, which would drop the Strehl ratio to below 0.7 before aberrations are even considered. I doubt that a real world specimen would have a Strehl any better than 0.6, probably closer to 0.5. Whether such a scope has enough contrast for a "good" visual image would I guess depend on the viewers expectations.

Click to expand...

Supposedly, a 6 inch SCT will have contrast somewhere equivalent to a 4 inch ED refractor with superior resolution of detail, at one third the price, half the length, and about the same weight. The view looked pretty good for $369.
o

goldenarrow said:

Supposedly, a 6 inch SCT will have contrast somewhere equivalent to a 4 inch ED refractor with superior resolution of detail...
o

Click to expand...

This might work out with an obstruction closer to 30% and nearly perfect optics, but your scope has a 46% obstruction and in the real world commercial SCT optics are seldom better than 1/4 wave, more often worse. I suppose the debate will never end between advocates of big SCTs with compromised optics vs advocates of smaller APO refractors with well corrected optics.

tradeoffs

henry link said:

This might work out with an obstruction closer to 30% and nearly perfect optics, but your scope has a 46% obstruction and in the real world commercial SCT optics are seldom better than 1/4 wave, more often worse. I suppose the debate will never end between advocates of big SCTs with compromised optics vs advocates of smaller APO refractors with well corrected optics.

Click to expand...

Firstly, I must say that I appreciate your comments. It has made me refine some of my ideas. Secondly, I believe that there is a place for what I will call CAT scopes (catidiotropic - aka, mirrors) under use by actual birders in the field.

So, I was re-reading some things and say, of course, central obstructions reduce contrast. That is one of the compromises in the design. The optics are excellent in this model, many amateur astronomers who own both 4 inch high end ED telescopes as well as maksutov and SCT (CAT) types are impressed with the sharpness of the images, both visually and photographically of the mirrored scopes. There is no argument amongst them that a $2000 100mm (4 inch) refractor will see slightly more shadings of detail (contrast) than a 6 inch SCT. But in resolution and brightness, the 6 inch SCT will equal or best the 4 inch refractor (unless it is a $5000 flourite refractor like a Takahashi or Astro-Physics). And you are right, this can be argued for years and I don't want to bother. All I want is an affordable way to view more of the bird, however that comes about (and the key word for me is affordable).

I have referred to the Better View Desired article in an earlier post.
Birding-Catidioptric-Scopes

I read it again and came across these interesting statements.

Regarding color fidelity:
"Mirrors, since they do not bend light at all, are inherently free of chromatic aberration and false color. What impresses birders is the all but perfect definition and delineation of each individual shade and tint in the image. The image in a scope like the C5 or Questar, or even the C90 with Special Coatings, can be breath-taking in good light, and will glow with subtle shadings well into twilight."

Regarding contrast and actual view:
"Thus the C5 should show the same amount of contrast as a refractor with a diameter of 3.1 inches (80mm) and the Questar/C90 would show the same contrast as a 2.375 inch refractor (60mm). That's theory. In my experience, once you get over about 90mm, the contrast of a properly baffled and coated Cat scope in full daylight differs very little from a prismatic refractor of the same or very similar size."

"....unless the refractor was exceptionally well corrected for chromatic abberation, the extra saturation and definition in the colors through the Cat might offset any loss of contrast enough to make it very difficult to say which provided the better image."

So, there is theory and then there is actual view with human eyes/brain which may compensate for the loss of contrast if there is a bright enough image. And the resolution is better, resolving USAF test charts to the smallest detail and resolution of less than one arc second. From the article a strong statement: "....The C5 resoloves finer detail than my test chart shows at 36 feet with the lines very sharply defined. There is little or no sign of the line blurring that results from abberations in the optical design. Outside, the C5 still resolves the finest lines on my chart at 66 feet, and might go a bit beyond. That translates to a resolution of .71 arc seconds, a fifth of a second better than theory, and more than twice the resolution of the best refractor that I have tested. You just can't get much better resolution than that! If you regularly need extreme high power to reach across a lake or tidal flat, I would have no hesitation in recommending the C5 as your best choice. Even if you are only going to use the scope at moderate powers, you really can not buy a better view at any price."

And then there are those on the forum who are using SkyWatcher 80mm refractors for photography and very happy with them. Certainly they avoid the problem of having out-of-focus donuts in the background. I already have an 80mm ED refractor that I use for hand-held photography and is very portable. But it is limited in power and brightness. The CAT scopes are an intriguing compliment to refractors. So, we can see there might be some interest in both kinds of telescopes used for birding, visually and photographically, especially since the connections and adapters are confusing to many people. A dedicated place to discuss things could be useful.

And downsides still include non-waterproof use and attaching to a photo tripod can be confusing if it only comes with an astronomy-style mounting rail (so a 5 inch CAT scope with a built in photographic mounting block would be more friendly). So, more discussion needed, not less.

Anyway, those are my thoughts and I hope to chronicle my experiments so everyone can learn from my mistakes and successes! Thanks for your patience in reading.

:t:

Cats fulfill the role other reflectors do: to get large aperture at low cost and size.
If the preponderance of the effect is to have higher measured resolution, there is
an interesting possibility: You can take a photo at 12-25 MP, downsample to 1-2 MP
(since that is all the PC screen gives you) with the right filter, and...reconstitute
the contrast and saturation you have have lost due to the design.

Everything has its tradeoffs: fast optics, for example, even with ED glass, torment
their eyepieces with the extreme light cone angles. It's strange sometimes to see an
ultra-short refractor with a massive and long eyepiece that is almost the same performance
as an astro just 5-6inches total longer (vs scope plus huge EP). The main difference could be
several thousand dollars. The long focal length of cats has an advantage at high power
similarly: even a simple eyepiece has tremendous performance.

There are many tradeoffs. I think the chief disadvantage, contrast, might be easily dealt with
by swapping the Cat's high light and resolution for high contrast and saturation.
I could do a photo if you have one. (Lanczos resampling down, contast+, saturation+, sharpen)

Short barrels do have a wide view, but that is mainly for lower powers.

I am into mid-length refractors, because the contrast exceeds both of the other types
(any short-barrel necessarily has its own issues with contrast),
but I came into a monster Cat. telephoto I want to convert, and they are a lot of fun.

goldenarrow,

I'd be more persuaded by your arguments in favor of the visual image quality of SCTs and MAKs if I'd never actually seen any. I've looked through quite a few from 70mm to 14" and never formed a favorable opinion of any of them, including the Questar. All have given the impression of looking at the world through layers of gauze, one layer for the best MAK's and several layers for the worst SCTs. The image quality of premium APOs, no matter what the size, has a transparency and vividness you never see in CATs, no matter what the size.

I also wouldn't take Stephen Ingraham's 20 year old review very seriously. .71" is obviously mistaken for the C5's resolution on the 1952 USAF. Telescopes just don't resolve line pairs "better than theory". It's also too bad he didn't have one of the really good APOs of the day for comparison. The Televue Pronto was a pretty ordinary achromat, yet he still found it equal to the 64% larger C5 for "brightness and contrast", something even I find hard to swallow and I'm the refractor guy.

Frankly I'm sorry I got into this. I feel like I'm raining on your parade when you're just having fun with a relatively inexpensive scope. I'm not sure you can do much better for $369 as long as the weight doesn't bother you. But, I don't like to see misinformation passed on, such as the notion that an inexpensive SCT will equal the image quality a 30% smaller premium APO. The first time you compare the Meade to one of those I think you will see what I mean.

Henry

Although the comparison with refractors for contrast seems like it was for
normal refractors. APOs now are all fast f-ratio, and by virtue of that aspect alone,
regardless of the glass or baffling, necessarily have lower contrast than a long refractor.

OPTIC_NUT said:

APOs now are all fast f-ratio, and by virtue of that aspect alone,
regardless of the glass or baffling, necessarily have lower contrast than a long refractor.

Click to expand...

Not true, OPTIC_NUT. I have a data sheet for an Astro-Physics 92mm f/5 APO. The Strehl ratio is 0.99. That's as good as contrast gets in a scope.

Strehl:

http://www.telescope-optics.net/Strehl.htm

I see a lot about abberations.
Astro-Physics relates it directly to the precision of the figuring.
"lenses will meet the 1/50 RMS (98.4% Strehl ratio) minimum limit." ??
Makes sense for a black sky with bright dots and no haze,
but it doesn't seem to add up for daytime contrast and it has no accounting
for baffling or stray light at all. Just RMS-->Strehl, nothing about the rest.

For daylight...I don't understand.
Any instrument with a wider field to start with has more trouble with stray light.
Unless you groom the surfaces very often to cleanroom standards,
I don't understand how all that can be put down to only the precision of the focus.
Even then, the objective precision still has only an indirect connection to stray light.


I'm reading it again:
http://www.telescope-optics.net/Strehl.htm
All of it is about the abberations and contrast of a point source, all the charts.

I am talking about the stray light and noise across the field.
I think you are as well, when you talking about the spiders of the reflector
scattering patterns. Strehl is an animal of quite a different stripe when it
comes to haze and noise and out-of-field light
or even structural diffraction in the daytime.

henry link said:

There's a very large central obstruction on that scope. Meade gives no spec for it, but I saw a reference that gave the diameter as 2.76". That would be a 46% obstruction, which would drop the Strehl ratio to below 0.7 before aberrations are even considered. I doubt that a real world specimen would have a Strehl any better than 0.6, probably closer to 0.5. Whether such a scope has enough contrast for a "good" visual image would I guess depend on the viewers expectations.

Click to expand...

But high Strehls seem possible in a reflector:

http://www.astromart.com/classifieds/details.asp?classified_id=762586

.95 for a 6.5" Mak-Cass? Maybe the size causes the problem,
but not so much the type. You just need more diameter. That matches the rule of thumb.

But...once again, the contrast I look for, in photos or views in daytime is not all tied to this.
Reflectors, fast reflectors, and fast refractors all have issues with stray light.
Strehl is a different circus.