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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 for the link, Paul. I had not seen this one. I have enough trouble hiking around with the Celestron 80ED or the ETX-90...can't imagine lugging that thing around! I purchased my Meade ETX-90 years ago on sale new for $399, at a time when you couldn't touch a short-tube ED refractor for that amount. I bought the Celestron 80ED new on sale at exactly the same price ($399) for digiscoping with an eyepiece and P & S camera. I saw your first post on using astro scopes without an eyepiece and a DSLR shortly after and you converted me :). Still like to tinker with the ETX though.

Keep tinkering, Rick. It's not only fun to do, but I find that I often surprise myself with unexpected results. Looking forward to seeing more shots, if you get out with the ETX.
 
Jason, i noticed on the Intes website that the Alter M500 can be fitted with an optional focal reducer of 0.55x which brings the f10 ratio to f5.5, but i assume this will also reduce the focal length too, from 1270mm to around 700mm ( 1270 x 0.55 )

Is that how focal reducers work ?

Can any Mak Cass scope be fitted with a focal reducer, and where are they fitted on the scope?
 
Yeah, the focal reducer also reduces the focal length by the factor of the reduction. They normally screw into the standard 1.25" filter thread of the erecting prism or the eyepiece. The best focal reducers are the ones designed for the specific scope otherwise you just use a generic one but risk losing out in image quality which can end up quite poor depending on the scope/reducer combination.

Paul.
 
Cheers Paul ... this is all curiosity only, as i havent even given the SW 600 f5 a decent workout yet. Got that DOI 1.5x TC to try yet - even got it in Pentax mount . Lucky or what
 
Paul is right, it's best to stay with the manufacturer/scope specific reducer, mainly because the optical math of the light cone modification is designed specifically for the respective scope...at least with regards to more complex optical systems like Cassegrains. What I mean by this is that a ƒ15 scope will react differently than a ƒ10 scope, etc... Also, for example, one manufacturer's ƒ10 MCT may have the eyepiece mount further back than a different manufacturer's ƒ10 MCT. Sometimes a few mm makes a huge difference in vignetting or ability to achieve focus, or both.

The following article explains the concept fairly well. Although it is geared toward Schmidt Cassegrains, and compares two different manufacturers' 0.33x reducers, the common factor of ƒ10 should keep most end results similar.

ƒ3.3 Focal Reducers
 
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Thanks for that Jason

Its just occurred to me that a reducer is not the same as a field flatener, but maybe you can get a reducer / flatener in one piece ?
 
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Cheers for that link to the Orion Al. I think f12 would be just too narrow an aperture for me. The 1500mm+ focal length is huge, and maybe hard to control...what do you think ?

Mind you, i know you can fit some kind of focal reducer to get the aperture down to f6 or f7 ( thats a guess )

On a bright day, I think f 12 shouldn't be a problem. Even f15 is OK but if you shoot from under the tree canopy, then it would be a problem. That guy Paul linked uses the Orion 1800 f 12, he also uses the C5 which is 1200 f10. It can be found at less than 200 Pound used. You don't carry a big bomb (where the camera body looks like the fuse for the bomb) and put something on to make it work like something smaller.....
 
Thanks for that Jason

Its just occurred to me that a reducer is not the same as a field flatener, but maybe you can get a reducer / flatener in one piece ?

Technically you are correct, Pete. However, I believe that focal reducers are usually designed to be field flatteners as well. As far as I understand the purpose of reducers came about for use with Cassegrain type scopes to convert them to astro-photographic lenses. With most Cassegrain scopes being a photographically slow ƒ10, the reducers brought about a means of significantly shortening the exposure times. Of course everyone here already understands that principle. But the additional problem of extreme field curvature (inherent to the very short focal ratio of Cassegrain primary mirrors -- typically ƒ2) necessitated the addition of field flattening into the design...again specifically for photographic work. The Meade and Celestron 0.63x pieces act as field flatteners. I think the Meade 0.33x reducer does the same. There may be some exceptions to this rule, so it's probably wise to research each reducer individually.

In contrast to this, I do have an Astro-Tech field flattener that is not a reducer, so it acts as a standard 1x device in the light path. However, the limitation is that you couldn't effectively use it on anything faster than about ƒ5.6.
 
Cant believe the guy on the website above is hand holding one of these beasts,i use one for birding and for extra length when needed,got some good results when the light is decent but always on a tripod,my arms would just drop off if i attempted hand holding..I use a Skywatcher 102 mak some shots can be seen here www.flickr.com/photos/apbirdman.
white wag,yellow legged gull in flight,oystercatcher,med gull and others all taken with this scope,also makes an excellent birding scope,coupled with an erecting prism and a decent lens and no CA at all..
 
I have tried very hard to use my C5 Cat for digiscoping. Poor images and low contrast. This doing indoor test images. Glare outdoor would be worse. Even if contrast could be controlled, the field has high curvature, even with a corrector. No way can it match the quality of my 80ED. Ok for visual, but not for photos. Gene
 
I have tried very hard to use my C5 Cat for digiscoping. Poor images and low contrast. This doing indoor test images. Glare outdoor would be worse. Even if contrast could be controlled, the field has high curvature, even with a corrector. No way can it match the quality of my 80ED. Ok for visual, but not for photos. Gene

Yours is a schmidt-cassegrain design. Maybe the Maksutovs are slightly better as far as photography goes regarding the points you mentioned. I think all the images and links in this thread are taken with Maks.

Paul.
 
Sorry folks,forgot to mention all pics taken with SLR attached to scope via a T-mount so not really digiscoping in the truest sense..the new lens I bought for the scope actually converts to a digiscoping lens,not really tried it out yet it screws straight onto the SLR via a t-mount,must give it a whirl to see what the quality is like
 
Here is another example of using a small mak scope for bird photography. This one was taken using a Celestron C90, 1000mm f11 mak scope. I am getting slightly better results using afocal digiscoping with this one with an old coolpix 995 and an 18mm scopetronix eyepiece. This is way more magnification than I would like to use with this old camera and scope, but it's the only eyepiece I have right now that will couple directly to the coolpix 995 without any adapter. The photo is uncropped, but adjusted for levels and unsharp mask in PS 6. Ancient everything technology on this one, hardware and software. I will attach a pic of the C90 for size.
 

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Is it the case with Mak-Cass , Schmidt-Cass or whatever , that if you attach a DSLR ( not a compact / fixed lens ) directly to the scope without DSLR lens or Scope Eyepiece or Prism, that subjects will be upside and back to front ?

This is something I like about refractors, in that direct mounting of my DSLR to the focus tube means i get the image the right way up, and orientated properly left to right
 
Is it the case with Mak-Cass , Schmidt-Cass or whatever , that if you attach a DSLR ( not a compact / fixed lens ) directly to the scope without DSLR lens or Scope Eyepiece or Prism, that subjects will be upside and back to front ?

This is something I like about refractors, in that direct mounting of my DSLR to the focus tube means i get the image the right way up, and orientated properly left to right

If you attach a DSLR the same way we do with refractors (without camera lens) then the image is right side up just the same as our refractors.
 
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
 
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