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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Example with a 90mm Maksutov-Cassegrain type scope (1 Viewer)

Thanks Blue - by the way, does the Mak Cass focus in a similar way to a refractor ? EG... 2 wheels either side of the focus tube for easy right or left handed people

Different scopes have different ways of focusing. The Celestron has a focus ring around the lens like a regular camera lens. The Meade ETX-90 has a small knob you turn on the back of the scope for focusing. That one is pretty awkward to focus and shoot at the same time.
 
Musoman,with a camera attached the image is the normal way around,dont know why this happens because to use as a normal scope I need to attach an erecting prism to right the image (the one that comes with the scope is the right way up but reversed left to right..confusing)
 
Musoman,with a camera attached the image is the normal way around,dont know why this happens because to use as a normal scope I need to attach an erecting prism to right the image (the one that comes with the scope is the right way up but reversed left to right..confusing)

You get erecting mirrors and erecting prisms. An erecting mirror will turn the image the right way up but it will still be wrong left to right. An erecting prism will turn the image the correct way up and it will also be correct left to right.

Astronomers prefer to use an erecting mirror because the light transmission is very high, around 98% of the light carries on to the eyepiece. With an erecting prism there is more light loss plus the chance of introducing unwanted chromatic aberrations.

The one that came with your scope would be an erecting mirror as the image is still wrong left to right.

With a camera like an slr I think the image is already the the correct way up when it hits the sensor. If you put an eyepiece straight into the scope then the eyepiece turns the image upside down again.

Paul.
 
Thanks Blue - by the way, does the Mak Cass focus in a similar way to a refractor ? EG... 2 wheels either side of the focus tube for easy right or left handed people

Most commercial Cassegrain types whether Schmidt or Maksutov actually use a knob on the back which moves the mirror up and down along the optical path. This is useful(for astronomy at least) in that you can put a lot of equipment such as filter boxes oroff axis guiders and still be able to focus as a small change in the distance between the two mirrors moves the external focus point significantly.
Drawbacks include changing the overall focal length-which may be noticeable if you focus on a close subject and a phenomenon called mirror flop-the knob usually is a spring loaded screw which pushes on one side of the mirror and this cause the image to shift to one side. This was very obvious with an old Celestron 8 that I used to own though more modern scopes seem to be better in this respect.
 
Another example using the Celestron C90 Mak. My practice pigeons were cooperating today. Taken using the Coolpix 995 and an 18mm Scopetronix eyepiece (archaic equipment I know). Distance was around 75 feet at a 35mm equivalent of around 3985 mm according to Jay's digiscoping calculator. Processed in photoshop 6. Not bad for this old play rig. Really to much magnification for this old 3.3 mpx camera, but this eyepiece is all I have right now to digiscope with this outfit afocally. For whatever reason I can't seem to get a very good photo with this scope at prime focus with my D2X.
 

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You get erecting mirrors and erecting prisms. An erecting mirror will turn the image the right way up but it will still be wrong left to right. An erecting prism will turn the image the correct way up and it will also be correct left to right.

Astronomers prefer to use an erecting mirror because the light transmission is very high, around 98% of the light carries on to the eyepiece. With an erecting prism there is more light loss plus the chance of introducing unwanted chromatic aberrations.

The one that came with your scope would be an erecting mirror as the image is still wrong left to right.

With a camera like an slr I think the image is already the the correct way up when it hits the sensor. If you put an eyepiece straight into the scope then the eyepiece turns the image upside down again.

Paul.

Cheers Paul - straight forward info
 
Most commercial Cassegrain types whether Schmidt or Maksutov actually use a knob on the back which moves the mirror up and down along the optical path. This is useful(for astronomy at least) in that you can put a lot of equipment such as filter boxes oroff axis guiders and still be able to focus as a small change in the distance between the two mirrors moves the external focus point significantly.
Drawbacks include changing the overall focal length-which may be noticeable if you focus on a close subject and a phenomenon called mirror flop-the knob usually is a spring loaded screw which pushes on one side of the mirror and this cause the image to shift to one side. This was very obvious with an old Celestron 8 that I used to own though more modern scopes seem to be better in this respect.

I see - thanks Phil

In which case, i'm wondering if the modern Celestron C5 has sorted out that sort of focusing problem, because in my searchings, the C5 is the only Scope i have any interest in. Its also been given the XLT coating that old version never had.

Maybe I'll try one out in the future at some point. Just thinking ahead really
 
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:smoke:

I have little money anymore to experiment Al, so not yet. Its very interesting to read about the Mak Cass scopes though.

Maybe in the future, but it seems the quality Mak Cass scopes are not cheap.
I looked at the Intes Micro russian models and the smallest Alter M500 ( 127mm / f10 / 1270mm focal length ) was nearly £800

Ok, its incredibly cheap compared to the top Canon L glass like the 600mm f4 and 800mm f5.6 but when you are used to only spending £250 / £300 on scopes like my current SW 120 and previous SW 80ED, £800 seems like another league

http://www.intes.su/goode.aspx?d=1

http://www.astronomics.com/main/pro...e/U5QNWB3RKWWL8N3EL99F9DX9A0/product_id/AT6RC
Is this cheap enough? No idea how well it perform LOL.
 
I think it would be too heavy ( i couldnt find info on the weight depsite a lot of searching ) - its quite long too at 20" although shorter than my SW120

The design of RC's seems to be far better than Mak or Schmidt for CA correction, + there's zero mirror flop
 
I think to even consider a scope like that then you need to be able to get it down to 500m or 600mm which would require something like a 0.4X reducer. But then it's probably a compromise as a focal reducer will likely drop the image quality.

Paul.
 
Apparently the RC scopes are better than MaK Cas or Schmidt Cass for photography...so i read anyways

As for weight, some serious guys lug around Canon L 600mm f4's and Sigma 800mm f5.6s ...somehow they cope, as the Canon is a tad under 12Lbs and the siggy is tad under 13Lbs , so on a par with the Astro Tech RC 6"
 
What makes this scope better than the Maks,do you still get the bad "Bokeh" spend most of my birding from hides so weight isnt that much of a problem anyway,dont really walk anywhere these days..good price on this one though
 
From my limited knowledge, the mirrors are fixed, unlike Maks which move ( or at least the secondary mirror moves ) and can introduce mirror flop when focusing, which causes image shift.

I dont know how much of a problem this is with quality Maks and Schmidts though.

In reviews i read, the latest XLT coated lens Celestron C-5 doesnt suffer this, and it weighs half that of the Astro Tech RC at about 6.5 Lbs, and almost half the length at 11"

If was going to go down the Cassegrain route sometime ( or not ) i would be getting the C-5
 
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What makes this scope better than the Maks,do you still get the bad "Bokeh" spend most of my birding from hides so weight isnt that much of a problem anyway,dont really walk anywhere these days..good price on this one though

The bad bokeh is because of the design of mirror scopes so yes it would be the same with this scope. At the front of a mirror scope you have an obstruction which is usually the secondary mirror and this is what causes the donut bokeh. Like you said though, the price is good but add on shipping and probably some customs import duty to be paid and it could go up a bit.

Paul.
 
Remember looking at the C5 before I bought my Skywatcher mak scope,not sure what dissuaded me at the time,it was probably price,although i dont seem to remember the C5 being as expensive then as it is now
 
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