Image scale - Where do you put your barlow.

[1ponders] (Paul) · #1 01-05-2006, 10:26 AM

It's been discussed in a couple of threads here over time, but I thought I'd resurrect the advice with a couple of images for example.

If you don't use diagonal when imaging then this won't apply, but if you still like to use one then consider putting your barlow before the diagonal. You will get a considerable increase in image scale. As I don't have a powermate to try I can't say whether the same applies for them, though I can't see why it wouldn't.

The following two images are taken with a meade 8"sct in poor conditions. The first is with a 2X Celestron Omni barlow (achro) after the diagonal and the second is before the diagonal.

Both images have only had a rough run through Registax with no scale adjustment.

h0ughy (David) · #2 01-05-2006, 11:32 AM

yes the image scale is increased, but at the loss of brightness? Does processing help that factor out?

[1ponders] (Paul) · #3 01-05-2006, 11:40 AM

I didn't adjust any of the settings h0ughy, just swapped the barlow around. You are going to get a loss of brightness no matter what method you use to increase scale. All that would be needed is an adjustment of gain/gamma.

I learnt something else the other day to (the hard way of course. Is there any other way

) Normally I have my laptop screen pretty bright when I'm planetary imaging at home alone, but the other night out at Ron's I had it turned right down. This had a direct affect on my ability to judge gamma, gain, brightness, saturation etc in relation to my exposure and frame rate. Consequently when I processed them at home the results were not as I expected. Most ended up with some onion rings from being underexposed.

asimov (John) · #4 01-05-2006, 12:59 PM

Yes, I tried this only the other night. Took a shot with the SCT with only the 2X barlow & toucam then added the diagonal on top of the barlow & took another.

Turns a 2X barlow into a 3X or so they tell me.

ving (David) · #5 01-05-2006, 01:21 PM

looks to be that way asi

insteresting how the barlow placement changes things likethat, but when you consider that the EP/webcam is further away from teh balow it makes sense (yeah i know, stating the obvious!

)

davidpretorius · #6 01-05-2006, 02:53 PM

k3ccd is good with that meter and trying to get to 200 - 250.