Can I use a barlow with this setup?

[carldr]

Hi guys,

I have an Skywatcher Equinox ED80, and I'm using a Canon 500D for capturing images with it. I'm looking for a 2x (or perhaps 3x) barlow to use with this setup.

I currently have to use an extender tube between the telescope and DSLR to be able to bring it to focus. Will using a barlow make this problem worse, or will the point of focus be closer to the telescope with it installed?

Are there any particular brands of barlows I should look at (or more importantly, avoid)?

Regards,

Carl.

[sixela]

Well, what are you trying to take pictures of?

If you're doing deep sky imaging, there's little point in increasing your effective f/ratio. Yes, objects will appear larger, but you're going to make the Signal/Noise ratio of your subs a lot worse because of the slower f/ratio, and frankly, you have oodles of pixels on that sensor, so you're going to be better off simply cropping the existing image.

If you really want a different image scale, you'd be better off with another sensor with smaller pixels.

If you want to image planets etc., then you need another sensor (i.e., a webcam-derived sensor or a dedicated planetary camera) a lot more badly than a barlow, and then you need a barlow.

About the only application I can see for which a barlow makes sense is lunar imaging at a slightly large image scale (at a much higher image scale, a webcam/planetary sensor again makes more sense).

[carldr]

Hi,

It's just so I can image the moon and Jupiter (and I guess eventually, the other planets) so they appear larger than they appear in my images now.

I'm not interested in planetary imaging enough to buy another sensor for it, and I'm happy enough with my DSO imaging and I wouldn't use the barlow for that. I figured a barlow would be a pretty cheap way of increasing the image size, but again I probably wouldn't bother if I end up needing to add further extension tubes to achieve focus.

To see how Jupiter appears for me at the moment, see the attached photo. That's obviously cropped. So yeah, just after a cheap way of increasing its size.

Regards,

Carl.

[sixela]

Hi,

It's just so I can image the moon and Jupiter (and I guess eventually, the other planets) so they appear larger than they appear in my images now.

You're better off just buying a webcam or dedicated planetary sensor. Some are considerably cheaper than a good 2" barlow (try to find a Philips SPC900NC --it's harder to find these new these days but the 1.25" adapter is easy to find once you grab one--), and you'll be able to grab at 5/10fps and enjoy the wonderful world of stacking with Registax.

I figured a barlow would be a pretty cheap way of increasing the image size,

Well, it is. The easiest one to bolt onto a DSLR is the Baader VIP barlow, but it's decidedly not cheap. One advantage is that you can add T2 extensions to tune the magnification factor quite precisely, and it'll work fairly well up to 3x.

Or you can get a "regular" 2" barlow if you already have a T2 to 2" nosepiece; the cheaper really good one is the GSO ED model (like this one).

If that's not good enough, you're already thinking about a TeleVue big barlow, and that's definitely more expensive than a webcam plus adapter.

[lukebl]

DSLRs really aren't suitable for planetary imaging, and I wouldn't want to risk having one dangling at the end of a Barlow! Not only precarious, but you will get sag in the system resulting in the sensor not being 'square' to the light path. You can use one at prime focus, though, for lunar and DSO imaging.

For planetary imaging you need a webcam (one of these -effectively the same as an SPC900 and cheap but very effective) or a more dedicated CCD. Believe it or not they will give FAR better results on planets than a DSLR.

[carldr]

Hi,

You're better off just buying a webcam or dedicated planetary sensor. Some are considerably cheaper than a good 2" barlow (try to find a Philips SPC900NC --it's harder to find these new these days but the 1.25" adapter is easy to find once you grab one--), and you'll be able to grab at 5/10fps and enjoy the wonderful world of stacking with Registax.

I can get one of those webcams for less than £30, so this is definitely an option I hadn't considered. I didn't realise such a cheap camera could be so useful.

Excusing my ignorance, how will this produce larger images? Is it purely that the sensor is smaller, so I end up with more pixels picking up the object?

Thanks for your replies by the way!

Regards,

Carl.

[riklaunim]

For pixel size in SPC880/900 you can use a Barlow with the cam to go up to f/20 at which you get the max of your scope. Some more modern webcams like Microsoft LifeCam HD/Cinema have much smaller pixels and they will get max out of a scope at f/10-f/7 depending on exact pixel size.

[sixela]

Is it purely that the sensor is smaller, so I end up with more pixels picking up the object?

Yes. The second issue is that they're made to grab very short exposures and to take movies (i.e. lots of pictures per second), and you actually need short exposures to "freeze" some of the bad seeing and stack a large number of images to piece together the best bits out of all the images. It's a fundamentally different technique to deep-sky imaging.

What you can expect from this camera is roughly this:

http://lxd55.com/?l=/astrophotos/ViewPhoto.asp&Photo=1718

If you want better images than that, you usually have to go to a similar sensor but in black and white (more resolution) usiing RGB filters to grab the different channels.

[carldr]

Hi all,

A SPC880 is winging its way to me, thanks to lukebl for the link - At that price, it'll be silly not to try it!

Thanks for everyone's replies and help, I'll post some pictures when I get some.

Best Regards,

Carl.

[philming]

Hi all !

I have a basic Toucam Pro that I thought I'd use as a guiding cam. Would the SPC880 be any better? Thanx for your help !

[lukebl]

Hi all !

I have a basic Toucam Pro that I thought I'd use as a guiding cam. Would the SPC880 be any better? Thanx for your help !

I think the Toucam and the SPC880 are essentially identical, with the same chip? Others may confirm.

I use my SPC880/900 for guiding with an ST80 guide scope, which works fine.