| Do you use the 0.7x/f3.9 reducer with your Askar Fra500? | |
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| Yes | |
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| Sometimes | |
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In my opinion, it takes far to long to adjust spacing on reducers to get correct backfocus. Rarely is the stated backfocus correct (enough). In this case, I would likely buy a Redcat or smaller Askar to increase FOV, than a reducer, just my general opinion. Cameras are so refined now, that a great deal of cropping can be done while keeping the pixels hidden on most displays if the FOV is too large. Just my experience. Hope this helps, Dave |
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The Askar FRA500 Quintuplet Astrograph is so clever designed that no spacers or calculations are needed. Switching between F500mm f/5.6 and F350mm f/3.9 is a matter of 2 minutes, given the fact that the so called (three-part) conus is readily prepared to do exactly this. This perfect solution was the very reason for me to buy the Askar FRA500 Quintuplet Astrograph - I know have two fast refractors with excellent performance which are easily switched in very short time. WITHOUT REDUCER - all three cone rings are used:  WITH REDUCER - only the biggest cone ring is used:   Every part needed is included - nothing else required (except the reducer, of course). < = > |
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David Payne: It’s super easy to get the 55mm back focus from the reducer. Just use the ccd spacers supplied by ZWO. Happy to assist, Dave. My only issue with the reducer paired with Asi2600 is images are slightly undersampled but that can be corrected in post-processing. |
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The Askar FRA500 Quintuplet Astrograph is so clever designed that no spacers or calculations are needed. Switching between F500mm f/5.6 and F350mm f/3.9 is a matter of 2 minutes, given the fact that the so called (three-part) conus is readily prepared to do exactly this. Oh this is new. I haven’t seen the conical adapters used to incorporate the reducer in such a way. I usually have the reducer adapter attached to the scope then the reducer then 55mm bf. |
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Andy:David Payne: That's great for you, and you will likely get good results with an APS-C camera. However, in my experience the backfocus of reducers is rarely within 1mm of the advertised value and this will be much more apparent with a full frame sensor. So I think it depends on your situation. If you are travelling, and you want the minimize the equipment you travel with, then a reducer may be a good solution so that you can change your field of view with one telescope. If you are a back-yard imager and may want to switch between APSC and full frame, keep the glass down, don't want to also fiddle with spacers w/wout filter wheels, off-axis guiders, and associated spacers needed to get exact back-focus then it is just a headache to me. If you plan to use mono/OSC and APS-C/full frame and OAG/guidescope and there are a lot of combinations of spacers to keep track of. I like Petzval telescopes because I don't have to worry too much about backfocus when changing my imaging train. Putting a reducer on it might be a convenience when travelling, but it kind of defeats the purpose of a Petzval. You might as well use an APO triplet. Having said that, one you do get the backfocus dialed in (as I eventually did for my wide-field corrector on my Televue), they can work extremely well. I didn't mean to offend. I have two Askars (the 500 as you do, and the 151phq) and I love them both. I just don't have the reducers for them. Why do I have the Askar 500 as well as the Televue despite similar focal lenghts? - simply because the Televue is a big heavy for my HEM27 mount. If I want a larger FOV, I turn to the RedCat. Bottom line is that with your 2600MC, the reducer will likely work well for you and if you try a full-frame may you will be lucky and the stars will be perfect corner to corner at the stated 55mm backfocus. |
