But usually, it's much easier to use a lens at a slower f/ratio than it it was desingned for, than to use it at a faster f/ratio.
For the adaptation to SC-threads or 2"-focusers, please take a look into the manual which you can find in the download section of the website.
We do not sell these spacer rings alone, but maybe TS has them or even includes them with their Special Edition.
For purchase in/delivery to the United States, please contact our distributor www.alpineastro.com.
Specifically, I have an AG I want to use again after a pause of a few years. It is currently in a 2" push-fitting without spacers which attaches the telescope to a Starlight AO unit, OAG, filterwheel and 694 CCD. The total from the back glass of the AG to the chip is about 129mm with the most compact connections I've found, or 8mm more than ideal.
I think for this reason, someone once told me to place the AG behind the AO and in front of the OAG/Filterwheel/CCD. However, this seems to me to be less than idea too. At the time, I ended up not using this set-up much in favour of the Hyperstar because the OTA was on a Fork-Wedge combination and quite wobbly. I have now deforked the OTA and put it on a decent EQ mount - so want to try this set-up again.
So my questions are: what is the best configuration? In the back of the optical tube inside the push-fitting with the 129mm to the chip or placed behind the AO and then at the "ideal" 121mm from that point? And what is the relation between the 146mm and 121mm?
The back-focus of an SC of about 146mm is the distance from the telescope's rear cell to the focal plane if there are no other lenses. If you use the Alan Gee, you place it in the desired distance from your camera (to achieve the desired compression ratio) and then focus with the telescope. Moving the main mirror changes the focal ratio of the SC, the data given in the manual refere to the resulting focal lengths when the Alan Gee is mounted as described in the manual.
But please note that the Alan Gee was designed years ago for Schmidt Cassegrains and not for the already flat field of an EdgeHD. For photographic use with an EdgeHD, we recommend the original Celestron reducers which were designed especially for the EdgeHD-optics.
The Alan Gee works fine with classic SCs, where it flattens the field and suppresses coma over a field of ca. 18mm - but with larger chips and smaller pixel sizes, this system is pushed to its limits. It is not recommended for pixel sizes smaller than 6-7my.
But for both EdgeHD and Schmidt-Cassegrains, the Alan Gee is a very interesting product for use with binocular viewers like the MaxBright II, because its working distance matches the back-focus of a binoviewer very good. Furthermore, the optical system of both Schmidt-Cassegrains and EdgeHD provides such a large back-focus, that the Alan Gee can almost double the field of view on most Celestron Schmidt-Cassegrains without visible vignetting. In the course of the development of the MaxBright II binoviewer, we have also developed a new T-2-cell for the Alan Gee. This new product - the AG Universal II - is designed for visual use with binoviewers and works even a little bit better with EdgeHDs, as they have a longer back-focus.
The AG II Universal as special reducer for binoviewing (but not for photography) will come to the market some months after the MaxBright II. If you are interested in binoviewing, we'd recommend not to buy the standard Alan Gee, because it deosn't offer the same connection options as the Alan Gee Universal. The Alan Gee Universal will be mounted directly between the binoviewer and the T-2-star-diagonal. We are looking forward to present this new product in 2020.
Thanks a lot
Also, If I want to use the Alan Gee telecompressor for Prime photography using Barlows / Eyepiece Projection, do I need to get additional adapters?
We have described them in the manual at https://www.baader-planetarium.com/en/downloads/dl/file/id/213/product/1197/baader_alan_gee_ii_telecompresor_shapley_lens_f_5_9_manual_and_applications.pdf
To use it with any of our 2" star diagonals, you need (as shown in Fig. 3 on page 2 of the manual) to remove the 2"-nosepiece from the mirror and replace it with
1) Baader Expansion Ring 2"a/T-2i with 1mm optical path length (T-2 part #28) # 2958242
2) the Alan Gee (you may have to remove the two extension tubes to achieve the best distance. The 2" Clicklock mirros has got an optical length of 112mm, so you probably have to remove both)
3a) Baader 2" / T-2 Nose Piece and Camera adapter (same as used by SBIG) (T-2 part #16) #2408150 if you want to insert the star diagonal into a 2" eyepiece holder or
3b) Baader T Adapter (BTA) for SC and MAK Telescopes (T-2 part #21) # 2408160 if you want to screw it directly onto your C9 1/4.
If you want to insert the Alan Gee into the telescope itself, you need the Centering ring for Alan Gee II Telecompressor # 2454410 (for C9 1/4), then you can lock it in its position with the standard visual back of your telescope.
I would not recommend combining the Alan Gee with a Barlow lens - you would use one optical element to shorten the focal length and then another one to extend it again. You'd be better of if you use instead one Barlow and adapt its magnification. The Q-Barlow 2.25x / 1.3x # 2956185 e.g. is designed for 1.3x or 2.25x, depending on where it is mounted, and the VIP 2x modular barlow lens, visual and photographic # 2406101 is designed for magnifications of 2x and more, depending on the distance. For calculating the different Magnifications with the VIP-Barlow, please check this PDF: https://www.baader-planetarium.com/en/downloads/dl/file/id/240/product/1062/calculating_different_magnifications_with_the_vip_barlow.pdf
EAN Code 4047825011572 Manufacturer Baader Planetarium SKU (#) 2454400 Weight (kg) 0.09 Optical length (mm) < 50 AR-Coating Multi-Coated (MC) Usage 8" Schmidt-Cassegrains Optical Design Field Flattener, Telecompressor compatible telescopes Schmidt-Cassegrain
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