SLR With Barlow

[Akyra]

When using my SLR and the x2 barlow - the only way I can bring the image to any kind of focus - I find that the image has too much magnification. The moon doesnt fit in the FOV, Saturn is great though.

So my question is, what do I need to bring the magnification down? I've heard of a 'focal reducer', does one of these do what I want? Can anyone recommend one?

Thanks, Ph!l!p

[Grant]

Phillip, can you unscrew the lens element from the bottom of the barlow? Leaving just the tube? This may work to bring the image into focus with magnifying it anymore..

Alternatively, you can get a focus extender, I've got a moonlite 2" that I got from Steve, works a treate!

[Akyra]

Yes I can, but how much I get the barlow to stay in the focuser?

[Akyra]

20 odd views and noone can help me out? Please guys...

[geppetto]

If you use a focal reducer, it will like as not bring back your

problem of not enough "in focus"

Only long term cure is to move the primary mirror up the tube

or maybe get a low profile focuser. Then you can do away with

the barlow.

It's a real pain, all my scopes have had this problem

[Nessy]

Hello,

like suggested I unscrewed my celesctron barlow so all I had was the smaller metal section containing the optics. I then put this in the visual back of my scope which is an SCT. This is different to you - will it go 'in' the focuser? If so, you can then put the SLR on and see if you can get focus. I had no problems when using the Celestron T-Mount and Adapter. However, too much power to get the whole moon in and you have to pan around, image and mosaic. To just take a pic of the moon I find staight-forward prime > DSLR or piggyback works a treat.

I am a real newb with all of this so there will be other much more experienced imagers who will direct you better.

[GazOC]

Nessy, SCTs have a lot more focus travel than Newts (Akyras scope), he doesn't have enough focus travel towards the scope before he 'hits' the tube. SCTs don't have this problem as they focus by moving the primary mirror.

[Nessy]

Ah - hence the focus extender?

[Akyra]

I dont fancy the thought of playing about with the primary, however my focuser isnt the best I dont think - having not used anyone elses.

If I could russle up some cash, I will buy a low profile focuser. I havent tried to image DSO's yet as I either dont have film or the clouds smother my sky, but I think they should fit in the FOV of the SLR.

I can unscrew the silver part from the black part, but unless I thread a silver bit of another of my eyepieces I wont be able to hold it in the focuser. Will that even work anyway? I would have thought like gepetto said, I will have the old problem of not enough inward travel - as there wont be any lenses (barlow lens is in the silver bit).

I tried a mosaic before, but all 4 images I took were blurred - My mount is useless for imaging.

Thankyou all for your help.

[Grant]

Akyra, on one of my barlows I can unscrew the black plastic bit that holds the lens from the bottom, this just leaves the top of the barlow and the silver tube that goes in the focuser, that way it gives the distance but not the magnification, this may not work in your case though but might be worth a shot...

[Akyra]

This is what I got to work with, if I unscrew the silver part I am left with the black part with the thumbscrew. The silver bit holds the lens, the black bit is hollow.

There is no way to keep the black part in the focuser, unless I screw a hollow silver bit off one of my EP's. I havent tried it but I'm guessing I wont be able to focus again - So I will try tomorrow afternoon.

Maybe buy a x1 barlow?

[GazOC]

Try the swap with your eyepiece, they are a standard thread. It might give you the distance you need to focus, the focus point will change in towards the telescope when you swap the lens out.

[barkis]

Akyra I think the best solution would be for you to join your local Astro Society and get some help there. The alterations you would need to make for your scope to do what you need requires alteration to either your main mirrors position in the tube, or the moving of your secondary mirror down the tube, which would also mean re positioning your focuser. In either case, you may get vignetting occurring if your secondary mirror is of a size that is too small for these fixes. The easiest way to do it is to move the main mirror up the tube a couple of inches, and not worry about the possible vignetting problem. The other solution I would advise against.

I sympathise enormously with you on the problems you are encountering, but you have to realize that a dobsonian, although a wonderful scope in it's own right, has it's limitations, and other than the moon and brighter planets, astro photography is off the agenda, without you carrying out major alterations to the whole setup. I know you won't do that. You can take good lunar pictures using eyepiece projection.

You can get great lunar pictures using prime focus. And, you can get good lunar pictures with Barlow projection.

What you won't get, and it hurts me to have to say it, is deep sky images. They require long exposures accurate guiding.

Use the scope as a visual tool. Get some good moon pics with it. Don't turn yourself off your your great scope. It will do what is capable of very well, but no more than that.

When you get through your education and get a good job that will earn you lots of money, you can then start to put the equipment together that I know you are yearning to have. Have patience. you can make it happen if you want it bad enough.

This is another saga I have written here, I hope you take notice of it.

Ron.

[GazOC]

Good advice Ron, enjoy the Dob for what it is - an excellent visual setup.

[Akyra]

Thats great advice Ron, everything you said makes perfect sense. I can enjoy the images that others produce. If I am totally honest, I really dont understand the whole imaging lark anyway. I have tried time and time again to read the Primers and other peoples writings but it goes over my head everytime.

I am quite content just to observe for now I think, cross my fingers maybe I'll win the lottery!

[GordonCopestake]

And just to add to what Ron said, it doesn't get dark enough for photography until at least August, so you have plenty of time to just enjoy the summer constellations