advice on first image with my c8 edge hd (odd star shape}

[iwols]

Hi all well after using my ts optics scope for 2 years ive decided to set my c8 up for imaging,imaging train set to the recommended 133.3mm backfocus ,and guiding was very good anyway a couple of questions someone may be able to help with

 

1..added a 5 min lum sub stretched ,stars are not perfect any advice

2..the c8 is f10 against my ts optics which was  f4 i believe what equivalent time do i need with the c8 for the same capture as the ts optics

 

thanks

Edited April 29, 2021 by iwols

[SyedT]

49 minutes ago, iwols said:

Hi all well after using my ts optics scope for 2 years ive decided to set my c8 up for imaging,imaging train set to the recommended 133.3mm backfocus ,and guiding was very good anyway a couple of questions someone may be able to help with

 

1..added a 5 min lum sub stretched ,stars are not perfect any advice

2..the c8 is f10 against my ts optics which was  f4 i believe what equivalent time do i need with the c8 for the same capture as the ts optics

 

thanks

Looks like a good start! The stars seem to have tails and are a bit triangular. Have you defocused and checked collimation is OK? This can cause the stars to have tails. Ensure that the secondary isn't too tightly held as anecdotally that can cause triangular stars.

In terms of light-gathering ability, an f/5 system would be able to gather the same amount of light in 1/4 of the time as an f/10 system, so I imagine it would take at least 4x as long. You have to factor other things in e.g. specific sky conditions on the night of imaging. I wouldn't worry too much about equivalence as the resolution you get is much better and so can see finer details. Just get as much data as you can!

Also, check whether you are oversampling, as then binning may help with star shapes and guiding: https://astronomy.tools/calculators/ccd_suitability

[iwols]

thanks not checked collimation will do tonight if possible,presume i leave the 3 locking bolts loose? i can use the image through my ccd to check collimation? thanks again

[SyedT]

3 minutes ago, iwols said:

thanks not checked collimation will do tonight if possible,presume i leave the 3 locking bolts loose? i can use the image through my ccd to check collimation? thanks again

The secondary screws need to be firmly against the secondary, but not overtightened. If you leave them loose the mirror will flop around, and too tight it may in theory cause stars to be misshapen. Yes you can use the CCD, although the issue is that the data transfer with CCDs isn't usually fast enough for you to have a "live view", and using images to do collimation can be very tedious. I'd advise you to do it with a high-powered eyepiece if possible if you don't have a CMOS camera with a USB 3.0 port.  Make sure you re-centre the star each time you make an adjustment or if it moves.

[iwols]

thanks thats great👍

[iapa]

https://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

 

[iapa]

25 minutes ago, iapa said:

https://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

 

Damn, didn’t notice the subject C8 EDGE HD.

In principle, tho’, go off focus and check the concentricity of the shadow and adjust.

https://www.celestron.com/blogs/knowledgebase/sct-edgehd-collimation-guide

[iwols]

4 hours ago, iapa said:

Damn, didn’t notice the subject C8 EDGE HD.

In principle, tho’, go off focus and check the concentricity of the shadow and adjust.

https://www.celestron.com/blogs/knowledgebase/sct-edgehd-collimation-guide

no probs thanks anyway