Which 3x Barlow for Planet Imaging?

netwolf · #1 20-08-2008, 10:18 PM

Hi All,

Would like some recommendations on which 3x Barlow to get for Planet imaging with a SCT? I have a C8 but will be looking to move up to a C9.25 or C11 some time down the track. Would the 40-50$ ones be ok for Imagin purposes.

Would a 2.5x Powermate be better? From what I have read the powermate was designed to overcome the impact of barlows on a longer FL EP's. So would it make much difference to small CCD sensors used for Planet imaging?

Regards
Fahim

Ian Robinson · #2 21-08-2008, 01:09 AM

I think 3x barlows are over doing it , the benefits from them have always seemed dubious to me.

You are limited by seeing conditions and the physics of optical systems (resolution).

Haven't used a barlow for many many years.

iceman (Mike) · #3 21-08-2008, 05:02 AM

It's for planetary imaging, Ian. A barlow is a must to get the focal length and image scale we desire.

Fahim I guess the $50 ones would be ok, you're imaging in mono so you won't get the colour spread that cheap barlows would probably give.

The 2.5x powermate is probably best, but with the filterwheel etc, you'll actually get less than 2.5x so you may not get the image scale you want.

Ultimately you may even want a 4x to get more image scale on those nights of really good seeing.

robgreaves · #4 21-08-2008, 08:40 AM

...for that very reason, the 5x Powermate is a strong contender.

A lot of the top planetary guys are using them. For instance, Damian Peach ends up at f/41 with his C14.

Regards,
Rob

Dennis · #5 21-08-2008, 08:45 AM

Hi Fahim

I’ve found the TeleVue x3 Barlow from Bintel to be a good performer. If you are going to invest the effort and time image the planets, then it’s worth using a Barlow with a pedigree. Otherwise you risk disappointment with poor results after all that effort in setting up, getting the planet on the chip, focusing, acquiring the data and processing it.

Note that I am not saying that the less expensive one’s are of poor quality, as I have no experience in using those brands. I just stuck with TeleVue as I knew I would not be disappointed having one of their components in the imaging train.

Cheers

Dennis

Dennis · #6 21-08-2008, 08:49 AM

My own experience with an x5 PowerMate is that I have only been able to use it for imaging reasonably bright double stars with my C9.25 F10, Mewlon 180 F12 and Vixen ED102 F9 refractor.

On planets or the Moon, the image just breaks down at F50, F60 and F45 respectively. I think that for my ‘scopes, an x3.5 PowerMate would be ideal for those nights of excellent, steady seeing.

Cheers

Dennis

AlexN · #7 21-08-2008, 10:35 AM

5x powermate can be useful, but you do have to watch your focal length on nights with less than optimal seeing... I have a 2x ED Barlow, a 3x TeleVue and the 5x TV PM, and since buying the powermate, I've not used the other barlows. However my scope only hits 6m focal length with the 5x, yours would be 10m plus whatever the extension of the filter wheel adds... Thats a LONG focal length.. It would only be useful on THE best nights of the year.....

I'd say get a 2.5x Powermate or a 3x TV barlow. If you have the money to throw around, get a 5x aswell, otherwise you'll get that night of brilliant seeing and be kicking yourself that you dont have more focal lenght.

netwolf · #8 21-08-2008, 10:49 AM

Thanks all for your advise, I have a 5x Powermate already and i find it to much for the C8 for imaging. It was more for my Dob and Refractors, which have shorter FL.

Mike for the last imaging run i did i used the 3x Tal barlow in front of the Filter wheel and I thought i was actually getting bigger image scale than I usually do. Even the Mono images i did where through the filter wheel with no filter in place in one of the slots. Compared to my previous efforts with the same barlow I feel that I am getting bigger scale. So If i used a 2.5x maybe i would get more. Not sure what the "reccomended" setup is perhaps i should be putting the barlow behind the filter wheel.

I could use the 5x in combination with the 0.63 reducer but more glass means less light. I fear 5x plust filters on the C8 will not let enough light through for good capture. I recall even with my Dob that Saturn looked really dim when cpatured through the 5x.

I am actually thinking of the 3x Televue Barlow which seems reasonably priced at Bintel compared to the cheaper variants. I am hopping with the 3x I can alwasy extend it to 3.5x or 4. Its a pitty there is no 3x Powermate. The nearest is a 3x 5000 series Teleextener from Meade, which i do recall reading may nearest in performance to the Televue.

There is also Sibert Optical's Telecentric barlows. But they dont have a 3x 1.25" TC version.

I think the TV 3x Barlow maybe the best at present. I dont want to splurge on the 2.5x powermate yet. Should have gotten it when the dollar was higher.

Regards
Fahim

AlexN · #9 21-08-2008, 10:57 AM

mmm a 3x will do you well. giving you 6m focal length before adding the filter wheel. I find 6m enough to get good image scale. obviously the longer you go the better, but with 8" aperture there is only so far you can push...

Alex.

iceman (Mike) · #10 21-08-2008, 11:06 AM

Fahim the 3x (or most other barlows including the 5x) with the extension of the filter wheel (or a diagonal) WILL give you more focal length (eg it might turn your 3x into a 3.5x or 4x).

However with the 2.5x, any extension will REDUCE the magnification - ie it might make it a 2x or a 2.25x.

Stephen65 · #11 21-08-2008, 11:18 AM

I have the TV 3x barlow and its an excellent unit. It's not that expensive and given how important the barlow is in your imaging train I wouldn't go for a cheaper unit. BTW if you own the TV 2x barlow and the TV 3x barlow you can mix and match them to make a 2.5x barlow, not that I've tried it but its been discussed on CN.

My main imaging scope is a 10" with a FL of 3m and I only occasionally get good enough seeing to use the 3x barlow for lunar imaging, usually I am using the 1.8x TMB ED barlow or the 2.5x powermate.

TrevorW · #12 21-08-2008, 02:14 PM

IMO get a 2 times then depending on where you place it in the focal plain you get 2 for the price of one.

matt · #13 21-08-2008, 06:34 PM

Quote:

Originally Posted by robgreaves

...for that very reason, the 5x Powermate is a strong contender.

A lot of the top planetary guys are using them. For instance, Damian Peach ends up at f/41 with his C14.

Regards,
Rob

Given that Damian uses a C14 (F10/11) that would mean he's using a 4x....not 5x powermate

I use a 3x Televue barlow almost all the time for my imaging....and it's great

And my imaging philosophy is: if the seeing's not up to using the 3x with my C9.25, filter wheel and DMK...then I'm watching TV instead!

AlexN · #14 21-08-2008, 06:40 PM

Matt, Matt, Matt... You're such a defeatist... (although your latest image shows why) Yes it feels better to produce good images, but it feels better again to at least be out with the scope practicing doesnt it?

matt · #15 21-08-2008, 07:12 PM

Alex...Alex...Alex

Not defeatism....just been there, done that.

I've done enough 'practicing' for the both of us.

I'm just a little more choosy now as to when I decide to image. I'm happy with that approach

Plenty of other guys share a similar philosophy. We keep a close eye on the weather maps and charts...take the time to familiarise ourselves with which prevailing conditions are most likely to offer reasonable conditions.

Each to their own, though.

That comment was half in jest, anyway.

Now, to which 'latest' image are you refering when you say my 'latest'? And how does that image reflect a 'defeatist' attitude?

AlexN · #16 21-08-2008, 07:23 PM

The latest Jupiter image , and it shows that the picky choosy approach pays off... (ie... it was a complement)

matt · #17 21-08-2008, 07:27 PM

The point, Alex...is that as far as I'm concerned, there's little point capturing RGB data of a fully jetstreamed Jupiter to 'practice' on.

The data is rubbish, and it doesn't offer me an opportunity to refine my processing skills.

All you end up doing is combining blurry red, green and blue blobs

Anyway...let's get not continue this here. It's a separate conversation for another time

Oh...and thanks for the compliment.

netwolf · #18 21-08-2008, 09:03 PM

Matt, yes i too am leaning towards the TV Barlow 3x. One point does anyone beside Bintel sell TV Barlows?
Also does anyone know why Zeiss/Badder barlows are so expensive?

Regards
Fahim

Rigel003 (Graeme) · #19 21-08-2008, 09:06 PM

Fahim, I would look at 2x or 3x televue barlow. Avoid the 2.5x powermate as Mike has said. The important point to bear in mind is that there's a limit to the image scale you can achieve with any given aperture . Over enlarging results in an underexposed image, longer exposures and lower frame rates, all of which reduce image quality. For my C11, the limit is pretty much a 2x barlow and a small extension tube. More than that and I can't sustain 30fps and have a reasonably well exposed histogram. I think a 4x barlow combined with the extra length for your filter wheel and camera will be way too much for a C8.

netwolf · #20 21-08-2008, 09:16 PM

Thanks Graeme, yes need to keep that in mind also dont want too little light. This is why i dont use the 5x.

Does anyone use the University Optics Klee 2.8 or 2.2x barlows? Would it be worthwhile getting a 2" visual back and using a 2" adapter instead of a 1.25" The C8 max opening is 1.5" so you would not get full benefit of the 2" Barlow.

Stpehen I also looked at the TMB barlow and it looks like its a good choice, have you been able to extend its power up at all?

Regards
Fahim