+/- 5000 counts only for focusing? why the limitation? unusable with my rig

[kevin747]

i love sharpcap, but now i found this limitation in autofocus. my new focuser is essatto 2 low profile ln c-14 edge. my middle point starts with 213000 counts. i tried everything last night with 12 stars in FOV detected and no curve could be achieved. moving 2000 counts does not even barely change focus and at least 6000-8000 counts are needed in one direction to see change that would be detectable above seeing limitations. so +/- 5000 counts is a sharpcap limitation and not practical with this focuser. can you expand the number of counts for these new focusers with huge counts? why did you determine 5000 counts as a limit anyway?

[admin]

Hi,

having used about 3 or 4 different motor focus systems, I don't think I've ever got past about 40000 or 50000 steps for the whole range, so +/-5000 seemed fairly reasonable for the amount to focus over. It's obviously fairly rare to be using such big ranges, otherwise it would have been picked up before now, but I can easily increase the maximum ranges.

From your description, it sounds like 10000 might still be marginal, so I will change to 15000 for now and we can see how that goes.

cheers,

Robin

[kevin747]

Awesome Robin! Thank you so much for the speedy response! This may help other users as well with the deep sky planner and similar focusers. Cant wait to test it out!

[nexusjeep]

Hi Bit late to this one I have the Esatto 4" focuser and mentioned this issue quite a while back but in the sequencer you can enter values larger as I have two scripts one at +/- 15,000 with 12 steps and one +10,000 / - 15,000 that I use once I have focus and am adjusting for temperature change and they produce a good curve and good focus. I can't remember whether I edited them in notepad though to do this.

Cheers
Nick

[admin]

Hi,

I think that you would get away with manual edits beyond the normal range as long as you just run the sequence. If you load the sequence into the advanced editor (or just view it there) then I think the values will get reset to the maximum range. Anyway, the latest updates allow a range of 15000 in each direction, which should be sufficient.

cheers,

Robin

[kevin747]

Thanks Robin for the change, especially in the deep sky sequence, the easy one. Now the issue is the number of steps. Its limited to 50. These new hi resolution autofocusers have 300,000 counts and 2000 counts minimum on my rig to see barely any change in focus.(FL=3950) Can you increase the number of steps to say at least 3or 4 thousand? Backlash does not need changing, it can go up pretty high.

Thanks in advance!

[admin]

Hi Kevin,

I think you are misunderstanding the meaning of the number of steps - that's the number of points that will be measured, no the gap between them. That means that if you choose a range of 20000 and 15 steps, the measurement points will be about 1400 movement steps apart (the distance is calculated automatically from the range and the number of measurement points)

cheers,

Robin

[kevin747]

Thanks for the clarification Robin! Sorry for the misunderstanding!

[nexusjeep]

I tend to run my Essatto 4" with +10,000 to -15,000 so 25,000 steps in total with 12 sample points and it gives me a nice curve for the focus assuming you are somewhere near focus at the time. To get a starting point I have a text file that gives temperature and a step count so at 8.0c for the 0.75x reducer it would be 286,054 and for the 1x at 8.0c 552,246. But scopes vary so you would need to build your own table but using the reference value and the focus range for +/- I have never had an issue getting a good curve and focus.

Cheers
Nick