A drop in Temperature will impact the scope and focal length of a scope, thus the need to focus during the night as T decreases.
Using SG pro, you can focus every hours or two hours or as needed.
You can use the celestron focuser with sg pro or any other equipment or software to automate the process, with no need to supervise the process.
The focus is done using FWHM of stars in your image, so the need to understand the positioning of the equipment to the mm is not that important.
Good luck
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Rich Sky:
A drop in Temperature will impact the focal length of a scope, thus the need to focus during the night as T decreases.
Using SG pro, you can focus every hours or two hours or as needed.
You can use the celestron focuser with sg pro to automate the process, with no need to supervise the process.
Good luck Why every 1-2h. For SCT, you need to focus every 1-1.5 degree drop/increase. Oh, I forgot. It is better to use NINA. All the best!
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AnaTa:
Rich Sky:
A drop in Temperature will impact the focal length of a scope, thus the need to focus during the night as T decreases.
Using SG pro, you can focus every hours or two hours or as needed.
You can use the celestron focuser with sg pro to automate the process, with no need to supervise the process.
Good luck
Why every 1-2h. For SCT, you need to focus every 1-1.5 degree drop/increase. Oh, I forgot. It is better to use NINA.
All the best! I've set SGP to use temperature compensation during the sequence. I've calculated my compensation factor and thus the focus changes every frame. I also have it set to auto focus every 1 degree of temperature change. When the auto focus runs, it requires almost no change since the focuser was keeping up with the change. My TC is +185 steps per degree for the EdgeHD 9.25 and LiteCrawler focuser. Interesting to note that my TOA-150B has a negative TC.
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overall I see the external focuser as a "nice to have" but not essential piece of equipment. With the standard focuser and an EAF one can cope quite well, make sure that the last focuser motion is always counter clock wise, so you push the mirror. She main benefit of the external focuser is that you get rid of annoying image shift (and resulting problems with guiding when using an OAG) when you change filters. @GalacticRAVE Can you tell me more about the problems a little bit of image shift will have on guiding? I'd like to understand this problem fully to decide if a drawtube focuser would benefit me too.
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Hi John, when you focus with the standard Celestron focuser, the mirror ever so slightly tilts, resulting in a shifting of the image. More when you move outwards. less so if you move inwards as you push it against gravity. this also happens when you switch filters and use filter offsets. In case of an OAG, the image shift of course also applies to the guide stars, and the guiding software kicks in to move the star back onto its desired position - since the shift is rather abrupt and large (considerably larger than the usual shifts owing to seeing), this can result in oscillation and it takes a while for the guider to settle. Alternatively you can disable guiding before you switch the filter - and the OAG need some time to settle afterwards. I have an encoder mount and use fairly long exposure for guiding (like 5 sec - never have a problem finding a guide star in the OAG), and so the settling takes a while (a couple of exposures) - as I said annoying, but not critical. Matthias
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I use this exact setup with the ZWO ASI2600MC Pro to great success. Since that 2600's sensor is deeper inside than, say, the 1600 or 294 (17.5mm if I recall), I have to use the Orion Thin OAG in order to be as close as possible to the backfocus point. My focus changes very little with the mirrors locked, mainly just switching between filters, and even with an APS-C chip, the difference in focus point between filters doesn't seem to affect the star quality. I'd have to go do the math, but I'd wager it's only moving less than 1mm between the different filters, which is within the uncertainty of the exact backfocus. I have found the C9.25 Edge HD to be pretty insensitive to temperature changes changing the focus.
I will note that I had some problems with my Esatto connecting properly to my PC until I used external 12V power in addition to the USB-C, even when I was plugging it directly into the PC and not through a hub. Now I have very few issues – once in a while I have to go unplug and replug the power and USB, but that's like once every several months. Being on a powered USB 3.0 hub has helped with that I think. It has zero backlash and has been awesome.
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I use a Rasa and live at a location with very large temperature drop. Over time I discovered that focusing every hour was a waste of imaging time. The fwhm of the star may change by 0.01. like 1.9 to 2.0 and I could not discern an overall change of quality in the image. Can anyone show, the difference it makes in focusing at every frame. just curious to see
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Rich Sky:
I use a Rasa and live at a location with very large temperature drop. Over time I discovered that focusing every hour was a waste of imaging time. The fwhm of the star may change by 0.01. like 1.9 to 2.0 and I could not discern an overall change of quality in the image. Can anyone show, the difference it makes in focusing at every frame. just curious to see I have not used RASA cannot comment. For long FL, changes could be serious about 0.3-0.5”. Is it a lot? Yes, if aim is photographing details of galaxies, PN, etc. I guess RASA is used for WFOV photography. In such case plus/minus 1-1.5” doesn’t matter. CS!
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OK, so to add to my post above:
My current setup:
- Edge 9.25HD OTA
- Celestron 0.7x reducer
- Esatto 2" Focuser with appropriate adapters
- Celestron OAG
- Celestron M48 to M42 Adapter
- ASI1600
I have not had a lot of chance to image since the OAG was added, but here is an example image with the OAG in the image train:
=============================================================================================================================
My previous setup:
- Edge 9.25HD OTA
- Celestron 0.7x reducer
- Esatto 2" Focuser with appropriate adapters
- 30mm M48 spacer
- M48 to M42 adapter
, but here is an example with this setup:
In both cases, I have gotten great results. Of course, this is with the 1600 sensor, which is only a 4/3rds size, so that may help. Here is an example with the previous setup:
It is of course always nice to try to hit the backspacing exactly if you can. But that being said, it is maybe not as critical as a lot of folks would have you believe. Here is a technical article from Dr. Gaston Baudat, the founder and brains behind Innovations Foresight, the guys who make the ONAG (On Axis Guider). He went through the theory including the effects of seeing compared to the impact of imperfect EdgeHD backspacing. The conclusion that I got from it is you don't have to sweat every single millimeter of difference between the theoretical exact spacing and what you end up with...
See what you think after reading the article...
https://www.innovationsforesight.com/support/celestron-edgehd-back-focus-tolerance/
ML There's a 146mm of backfocus but when I add up your current setup (first image), the one with the OAG I get 2+67+4+29+11.5+20 and, for me, 17.5 for the ASI2600 camera. This comes out to 151mm, which is 5mm too long. Am I miscalculating? Jerry
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