Webcam and Barlow

[Altomar718]

Hi All - I am very new to imaging and astronomy in general and wonder if someone can help ..........

I took some avi of Jupiter last night and centered it as well as I could in Sharpcap and then tried to use a 2x Barlow but could not find it on the screen. I used the retiucle and cetered it using a 3.6mm eyepiece but still no luck ......

Is there any easy way of finding it when using a Barlow (if indeed you can use one with a webcam !!!)

Thanks

Chris

[Steve Ward]

Using the barlow will make the image a lot dimmer and way off focus compared to the view without.

I'd suggest turning the brightness/gain right up so that you can see the out of focus image a lot easier to start and then refocus.

[brucen]

As Steve has said it will look a lot dimmer with the barlow and need different settings. You will get better results with the barlow though and the attached link explains why.

http://www.project-n...cam_imaging.pdf

I use a 3X barlow now and it does take a while to find things but they are still there! Focusing also becomes harder as any tiny movement has the object dancing all over the place. I added an auto focuser to my scope when I started to use the 3X barlow to make it easier.

[Altomar718]

Using the barlow will make the image a lot dimmer and way off focus compared to the view without.

I'd suggest turning the brightness/gain right up so that you can see the out of focus image a lot easier to start and then refocus.

Steve - You have done it again - Thanks mate and I wished you lived near Bideford so I could come and hassle you with all my questiions !!!

Thanks also Brucen - I have read the document - interesting stuff. One thing it mentions is a good quality Barlow. I only have the one which came supplies with the Skywather scope, so probably cheap and nasty!!

Have you got any suggestions of a resonably priced Barlow (3x) - I did find these at Joys on Ebay with a good write up, but there again, its by the geezer selling them ! :-

http://www.ebay.co.uk/itm/1-25-3x-BARLOW-LENS-TELESCOPES-Best-Quality-NEW-/140604643588?_trksid=p5197.m1992&_trkparms=aid%3D111000%26algo%3DREC.CURRENT%26ao%3D1%26asc%3D14%26meid%3D5986707107592201972%26pid%3D100015%26prg%3D1006%26rk%3D1%26sd%3D140604643588%26

Thanks

Chris

[JamesF]

If you add some sort of extension behind the barlow you will increase its effect. The 2.5x barlow from Revelation works well. If you remove the lenses from your existing barlow so it's just an empty tube and insert that between the camera and barlow then the image will be larger.

It is tricky getting targets perfectly centred though, and when you start ramping up the focal length it gets even harder. I use a cheap illuminated reticle eyepiece for centering and it makes life much easier. I centre with no barlow, centre with the barlow, centre with the barlow and extension and then put in the camera.

It's also worth mentioning that the recommended focal ratio in that document may be misleading. The desired focal ratio varies depending on the pixel size of the camera. With (for example) an SPC900 it's probably f/30 to f/35, whereas with a Lifecam Cinema it's probably closer to f/20. Unless you're using a Mak or SCT you're probably going to struggle to get those kinds of focal ratios without a fair bit of practice, so just build up to it and bear in mind that if you overdo things you won't get an image that's bright enough to do anything useful with.

James

[Altomar718]

Just to say thanks for the advice and I have managed to actually capture something - I am pretty chuffed with it but I know members on here get superb results .......... but 1st attempt !

Used the 2x barlow and turned the gain right down - - - - - and there it was !!!!

[JamesF]

I'd say you could drop the gain some more, or increase the exposure time and up the frame rate, but it depends which camera you're working with. If you open the histogram in SharpCap (it's on the drop down menu next to the reticle option I think) then I'd say that ideally you want the graph to come 60% to 70% of the way across the window.

James

[JamesF]

Doh! I mean decrease the exposure time above. It's been a tiring day

James

[brucen]

I would be very pleased with these as first attempts! The quality depends not only on the equipment but on the viewing conditions as well - I have had quite a few nights where I have been convinced the pictures will be the best ever only to find that they are not! Keep at it and play about with the settings until you get what you want. It also take a while to get used to the processing.

My 2X barlow is a Revelation that was part of their eye piece kit and I was lucky to pick up a 3X Tal just before they became as rare as hens teeth. I get pretty good results with the Revelation and the 2.5X is regularly recommended.

[Grotemobile]

I use the Revelation on my set up as well.

What i have done is unscrewed the end

of the barlow & scewed it into the web cam.

This gives me a 1.5 barlow,which works out

at f15 on the C11 .This is about the most i

can use with this scope.

Steve.