Wide open with a cheap lens. Is it worth it?

[cuivenion]

I'm guessing the answer will be try it and see. I'm using this lens:

https://www.pentaxforums.com/userreviews/chinon-135mm-f2-8-multi-coated.html

and recently took this image stopped down to F4.66:

I'm wondering if I should stop down even more to get rid of the chromatic aberation, or if I should just get the most signal I can and use it wide open. I was getting quite large halos on the stars at 4.6 anyway so maybe I'm better off going for the max signal.

[alacant]

Hi. f5.6 should reduce the halos a bit but they're easily fixed by using a Wratten #8 or after the event by healing in software. HTH.

[cuivenion]

Thanks, I have and F8.4 circle cut out. I might see how that goes. Lets hope my guiding's up to 10 or 15 minute subs!

[happy-kat]

Looking at your link you have good star shapes corner to corner. If it is like my lens f8 won't stop the chromatic aberration. i have to process it out but rather have the light with wider aperture.

[cuivenion]

2 minutes ago, happy-kat said:

Looking at your link you have good star shapes corner to corner. If it is like my lens f8 won't stop the chromatic aberration. i have to process it out but rather have the light with wider aperture.

Thanks happy kat, I'll have to decide, I'm going out soon lol. Do you have any links of images you've done. If you have any tips on processing that'd be great to, if thats not to cheeky.

[happy-kat]

I either use f2.8 out stop it down one or two stops still experimenting to decide where is best for my lens. I posted two images in Here f8 just was too dim.

[alacant]

Hi. Here's my effort. A Porst 135 at f5.6; same lens I think. HTH.

[ollypenrice]

Try to focus using a star at the intersection of the 1/3 lines on the chip. This is incredibly effective. (A tip I learned from Peter Smith who hasn't been around here recently.)

Olly

[Atreta]

9 hours ago, cuivenion said:

I'm guessing the answer will be try it and see. I'm using this lens:

https://www.pentaxforums.com/userreviews/chinon-135mm-f2-8-multi-coated.html

and recently took this image stopped down to F4.66:

I'm wondering if I should stop down even more to get rid of the chromatic aberation, or if I should just get the most signal I can and use it wide open. I was getting quite large halos on the stars at 4.6 anyway so maybe I'm better off going for the max signal.

I have a tokina 135mm f2.8 lens and i have to stop it down to f5.6 to get rid of the chromatic aberration. 

[cuivenion]

It was very hazy last night unfortunately. Tried for m81 and m82 at 2.8, but my 3 hours of 3 minute subs were over exposed due to the haze reflecting light pollution. Thanks for the replies.

[cuivenion]

19 hours ago, ollypenrice said:

Try to focus using a star at the intersection of the 1/3 lines on the chip. This is incredibly effective. (A tip I learned from Peter Smith who hasn't been around here recently.)

Olly

I'm afraid you've lost me a bit here Olly. You'll have to dumb it down for me I'm afraid. ?

[happy-kat]

[cuivenion]

3 hours ago, happy-kat said:

Cool, I'll give it a go.