CCD + Barlow questions

[EricB]

Hi there,

I have indicated previously in a couple of posts the difficulties I have in using a Barlow in conjunction to my DMK 41 CCD camera when taking AVIs of the Moon (I have an off-the-shelf SW Flex 10" Dobsonian).

Basically, without the Barlow, I get data I am really happy with, and when I attempt to use my GSO x3 Barlow all I seem to get is a grey picture completely out of focus. A far cry from what I can get without the Barlow (and I far cry from the great Moon close-ups I see on the web).

Yesterday, I had possibly the best seeing I have experienced in my 8 months of photographying the Moon. The AVIs were of high quality and I gave the Barlow another shot. The resulting data was better than usual; however, it was still unfocussed. What I mean by unfocused is that there is focuser travel on each side of the picture, but this is the best focus point I can get.

I have attached a picture without Barlow and with Barlow of the Theophilus and Cyrillus for comparison.

My question are:

Is my Barlow low quality, therefore I can't achieve focus when added to a CCD?

Are Barlows only usable in exceptional seeing conditions and I should only bother fitting it on those few days a year?

Or, as I suspect, is it a bit of both? In which case, I should invest in a better Barlow (eg a TV Powermate x 2.5).

Am I missing anything obvious ?

I would be very grateful for your comments. Thank you.

Eric

[Larryp]

With a 3X Barlow, I think you may be going for too much magnification.:)

[Screwdriverone]

Nope,

I think its a crap barlow.

My GSO seems fine, but I think that one may be suspect if you still have focus travel on each side of what seems the "best" focus.

Try another one if you can.

Chris

[loki78]

Try an eyepiece with roughly the same magnification as the fov off the dmk suggests with the 3x barlow and see how that looks.

Try to borrow someone elses barlow if you can as well to rule it out as chris suggests

[EricB]

Thank you for your comments and suggestions.

I have used the eyepiece + Barlow combination with variable success in terms of quality (usually 15mm + Barlow). It's never been great (but then again its the equivalent of a 5mn piece). I would say, my 6mm GSO consistently gives me a better picture than the combo.

I wonder then how some of you manage to use CCD + x5 Powermates on planets with such great success!

Cheers,

Eric

[Poita]

A: A better barlow/powermate, electronic focuser, fast framerates, thousands and thousands of frames, cooling to stop tube currents, waiting till the planet is directly overhead and waiting for those few nights a year of great seeing.

i.e. perserverance and luck :D

[Poita]

I can loan you a televue 3x barlow to see if your GSO is the problem.

[Shiraz]

did you use a slower exposure for the hi mag image? - if so you would have more blur from seeing. But I agree, it does look like an underperforming Barlow.

FWIW, I had 3 GSO Barlows over the years. A 5x was so bad that it had to be replaced and the replacement, although generally OK, still would not focus quite well enough for hi res imaging with my f4 scope. A 2.5 was sharp, but had a tiny bit of wedge somewhere which resulted in detectable colour fringing. My 2x 2" is excellent and only just a slight bit behind my TV big Barlow - I use it all the time for visual. In my experience, GSO Barlows can vary a bit in quality.

If you are using the standard Plossl eyepieces that come with scope packages it is worth getting a good Barlow, since the Barlow can improve the performance of cheapies, presumably by reducing the light cone angle that they have to deal with (quite a large improvement is possible). And a good Barlow is essential for hi res imaging. I found the 3x TV Barlow to be excellent and it would probably be a good match for your scope. You can get out about 5x if you use an extension tube (which you can make by taking the glass out of your existing Barlow if it turns out to be inferior). regards Ray

[ZeroID]

Sounds like my problem, a crappy barlow. I didn't think you could make such poor optics but it seems to be the case. Seems to never reacha good focus. I'm giving mine one last chance to redeem itself before i buy something that works.

[LewisM]

The Shorty 2x barlow I have from Orion is mediocre. Not that I use it - not much use for DSO's ;) Undoubtedly made by GSO

I have never had much success with GSO unfortunately. The FR they make for Orion I have my suspicions on too - seems to give my ED100 "pinched" optics look to photos that are NOT present without it. (I ordered a genuine SW FR made specifically for the ED100 instead now). Plus, EACH of the drawtube extensions from GSO I have SEEM fine, until you release the weight being supported as you tighten the thumb screws - then it sags, and you get misalignment. NOT impressed thus far, hence never ordering one of the RC scopes yet. Cheap is as cheap does I guess, but I am being subjective and your result will undoubtedly vary.

[EricB]

Thanks everyone for your feedback.

Yes, it's a bad barlow.

LewisM and Shiraz: Interesting what you say. Of the 4 GSO eye pieces I have, the 10mm is the best. It's actually not that far behind the ES 11 mm I have just bought. The 25 and 15mm or pretty average and the 6mm is ordinary. There seems to be some inconsistency between GSO products. For a bit more money, I have bought myself a 6mm TMB Planetary II which is much better.

Loki: I have tried what you said tonight. The result is still poor. So a bad barlow it is.

Peter: I wouldn't mind trying your barlow. Do you still have my address?

Cheers,

Eric

[Poita]

No, I don't think I have anymore, drop me an email and I'll post it today.

[Shiraz]

Good to have that sorted.

My eyepieces are also variable, except my 6mm is the very good one - and they all work OK with a Barlow. However, for the intended purpose and for the money, most GSO gear works very well. I guess it was a bit unfair and misleading to compare their products with those costing 5 times as much, as I did in an earlier post.

[EricB]

You are right Ray. GSOs are still very useful as a first set of eyepieces until we get better ones. They are very good value for money. Funny you say that your 6mm is fine. Mine is the worse of the lot. That's why I have upgraded it to a TMB which is twice the price, but it's not twice the difference ;). Still it's better.

Cheers,

Eric

[brian nordstrom]

:thumbsup: Good luck Eric , on the barlows I have a GSO 2x and a Celestron Ultima 2x and there is no comparisim between these two , the Ultima is way , way better .Needless to say the GSO only gets used when the public is around ,;) .
Brian.

[EricB]

Thanks Brian. I tried the GSO barlow again tonight under good viewing conditions. It's absolutely useless for astrophography.