Using a barlow for imaging.

[oldfruit]

Hope i don`t sound thick here.

I currently use an f5 newt with a canon 100d on a driven eq5 for my attempts at imaging. Trouble is that some objects are quite small and i would like if possible to use a barlow with the above kit to give me a bigger image.

Trouble is that my scope being an f5 would with a 2x barlow become an f10? This would mean a slower scope so i would need to capture more subs to aquire a decent image? Also the fact that i use an eq5 means that currently i can manage reasonable subs of about 60 sec max before any really noticable trailing.

Would it be worthwhile trying to image with a barlow or in your experiences would i be wasting my time.

Hope my question makes sense.

Thanks Mark.

[Doc]

I'm not an imager but your calculations are correct, F5 + a x2 barlow would mean an F10 scoope, which then would be x2 slower as well. So to capture the same amount of detail your 1 minute exposure would need to be 2 minutes instead.

[oldfruit]

Thanks for confirming that Mick. So basically as long as my mount tracks well enough at the increased magnification, twice as many 60 second exposures should give a similar result?

[Doc]

Yep that should do it.

[Perkil8r]

I asked a similar question the other week. Apparently though, exposure times wouldn't need to be doubled, they would need to be 4 x as long! On a good night, with near perfect Polar Alignment I can push my 200p on eq5 to 80 secs before trails become an issue.

[oldfruit]

I asked a similar question the other week. Apparently though, exposure times wouldn't need to be doubled, they would need to be 4 x as long! On a good night, with near perfect Polar Alignment I can push my 200p on eq5 to 80 secs before trails become an issue.

4x as long or 4x as many subs. Wow that would mean a long imaging session. I have on occasion gone for longer subs and they do come out ok but to try to get the best results i have tried to limit myself to 60 seconds. I do spend a while doing my polar align each time and get it as bang on as i can so this always helps.

[Perkil8r]

I'm not 100% sure, but think it was 4x the exposure length rather than number of subs. I've not tried though, so it might work well. I was considering trying with M51 and or M27 with the barlow as I wanted them to be bigger. One thing I did think though, is that any amount of error is going to be magnified too, so star trails may well show up worse or at shorter exposure lengths. Try it and see, it's not like it's going to cost anything to try.