Problem

brandmandsam

How Can i solve this problem? Somebody told me that the Camera 294 c pro Will hit the fork Mount when P.A. With the asi Air pro

the Camera needs a 105mm of back focus.

this is my GPS
Latitude: 55° 03' 35.35" N
Longitude: 10° 36' 24.37" E

w7ay

brandmandsam How Can i solve this problem?

How close can you get to the pole before your instrumentation hits the base of the fork? If you can get past +60º north (for example, Dubhe), you can use ASIAIR's polar alignment tool. You do not need to be at +90º declination to do polar alignment in ASIAIR; you can be up to 30º in declination away from the pole.

But be very careful. Your set up is an accident waiting to happen -- even when not doing polar alignment near the pole. With a wrong GOTO path (which happens often in ASIAIR if you frequent this forum), you will destroy both your camera and fork, and most likely the OTA's visual back, too.

Defork it, and mount the OTA on a German mount. You eventually will be forced to anyway, when an accident happens; at that point, your OTA may not be salvageable.

You might also check if the FOV of your combination is not too narrow for ASIAIR to do a plate solve. ASIAIR needs to plate solve during the polar alignemnt process.

Chen

brandmandsam

w7ay

Thanks

I can make it almost straight up in the sky. So almost in home position. I am missing 3 - 5 cm approximately.

What do others do with Meade and fork mounting. I know there are several who have the same setup as me.

And ZWO has said that Asi Air lasts with a Meade Lx90 fork mounting

What about a diagonal... But how do i then 105 mm of bac focus

w7ay

brandmandsam What about a diagonal...

Diagonal mirrors will usually produce image tilts. Truly bad idea for imaging.

If you can clear with a diagonal, at least it will be safer than what you have right now; you just get crummy photos. But once you introduce large filter wheels and such, you are probably back to the same predicament with a fork. There is good reasons why astrophotograhers stay far away from a fork.

If you are dead set on using the Meade fork (remember, bad idea), and if you have a view close to the NCP, mount a polar camera to the fork arm itself. It can be small finder/guide scope with a ZWO camera. There will likely be a lot of cone error, but ASIAIR's polar alignment process will not care. Just make sure you remove the main camera before doing polar alignment; and keep vigilant each time you apply a GOTO, to make sure the instrumentation does not hit the fork.

Chen

Markus

I am wondering about about your back focus. Usually the back focus is about 85 mm (end of 2” SCT) with the corrector you are using, 20mm less than your setting. My 50 easy cents: take out the corrector for polar alignment, and put it back afterwards, takes time but you are safe. If you get no tilt with corrector camera design, then it should work properly. The back focus is usually not defined by camera but by the corrector you are using. Use another corrector like the Baader Alan Gee that is positioned further inside the tube and You will safe you several cm.

regards Markus

w7ay

Markus Usually the back focus is about 85 mm (end of 2” SCT) with the corrector you are using, 20mm less than your setting.

If he is using a "standard 0.63x" reducer, then 105mm is the correct backfocus.

The 105mm number originally came from the use of a 50mm (2") long SCT-to-T2 adapter, plus the 55mm "standard." So, the original 0.63x reducer from Celestron back then had 105mm backfocus.

I still have a 0.63x SCT reducer that was manufactured in Japan, instead of the stuff from China today. The modern Starizona reducers are better still.

Back before Hyperstars etc (about 15 years ago), I bought a special edition 8" LX200 with f/6.3 native focal ratio (still have that white elephant). Together with a 0.63x reducer, it gave me an f/4 system. Horribly narrow usable image circle though -- but back then, there were no full frame cameras anyway to need a large image circle; even in 2010, the SBIG ST-8300 was the largest sensor I had :-).

Chen