Teleview Powermate vs Barlow's + Effect on Focuser

Globular3 (Jeff) · #1 13-07-2008, 03:53 AM

Hi All,

I've searched the net a while now and can't seem to get the answer to this question.

"How does the focal travel get affected when using a barlow lens?"

I'm currently using the 1.25" 3x barlow supplied with the scope without any problems however, will I be able to use a 5x barlow with the 50mm travel that I have with my f/5 80mm refractor, or will I need some extra equipment? I'd just like to use it straight as it is without buying anything else with the barlow.

The 5x Powermate says it is parfocal. Does this mean I can take out the already focused eyepiece, put in the 5x powermate, replace the same eyepiece and there's no need to refocus? If I understand this correctly, then the 5x Powermate would be the way to go.

Can any of you Teleview enthusiasts and eyepiece experts give me some help on this one please?

Regards,

Glob.

Dennis · #2 13-07-2008, 09:46 AM

Hi Glob

I think that Par focal is more a property of a range of eyepieces, meaning that when one eyepiece is focused, you can simply replace it with the next one and in theory, the focus should be spot on.

From memory, I don’t think that my TeleVue x2.5 and x5 PowerMates (1 ¼ inch) are parfocal – I recollect having to adjust the focuser when changing PowerMates with either a ToUcam or a DMK CCD camera plugged in.

I have a TeleVue x5 PowerMate in the 1 ¼ inch fitting and in my experience, I have only used it visually on my Vixen 102mm F9 ED refractor a few times, mainly to split double stars.

A x5 PowerMate will convert your 80mm F5 to an 80mm F25 system and you will probably be disappointed with the views?

Cheers

Dennis

Globular3 (Jeff) · #3 14-07-2008, 03:38 PM

Quote:

Originally Posted by Dennis

Hi Glob

I think that Par focal is more a property of a range of eyepieces, meaning that when one eyepiece is focused, you can simply replace it with the next one and in theory, the focus should be spot on.

From memory, I don’t think that my TeleVue x2.5 and x5 PowerMates (1 ¼ inch) are parfocal – I recollect having to adjust the focuser when changing PowerMates with either a ToUcam or a DMK CCD camera plugged in.

I have a TeleVue x5 PowerMate in the 1 ¼ inch fitting and in my experience, I have only used it visually on my Vixen 102mm F9 ED refractor a few times, mainly to split double stars.

A x5 PowerMate will convert your 80mm F5 to an 80mm F25 system and you will probably be disappointed with the views?

Cheers

Dennis

Hi Dennis,

Thanks for letting me know this info.. So I'd probably have to wind the focuser in a bit (I think this is the correct way???

) with the powermate. Also, I wanted to use the high power to resolve double stars, see better planetary detail and improve my lunar observations. The 3x barlow (even though its a cheap one) gives a real improvement to the detail. Bearing in mind that I don't need the rich field property of the refractor for this type of work, do you still think the 5x powermate (or barlow) wouldn't be a good choice?

Regards,

Glob.

Dennis · #4 14-07-2008, 04:16 PM

Hi Glob

I cannot really give you specific advice for your 80mm F5 as I don’t have one, so all I can say is that visually, on the Moon and Planets, the x5 PowerMate does not produce pleasing views through my Vixen 102mm F9 ED refractor. The magnified views are soft and do not reveal any further detail than the x2.5 PowerMate.

However, when the seeing is very still, I can use a webcam with the x5 PowerMate on the 102mm F9 but even then, only 4 to 6 times each year. The webcam can take 30 to 60 frames per second and when you align and stack them, produces a pleasing image because you can take advantage of those moments when the seeing becomes very good.

Cheers

Dennis

AlexN · #5 14-07-2008, 07:10 PM

Yeah I just got my 5x powermate, and do have to wind the focus inwards in order to focus an already focused eye-piece.

I visually used it once, and dare say I will not do so again... I bought it primarily for planetary imaging, and the views through it vs my 3x ED barlow were soft and somewhat lifeless in my 8" newt. however this could well have been due to the seeing conditions, which have been less than decent of late.

Globular3 (Jeff) · #6 14-07-2008, 07:46 PM

Hello Dennis and AlexN,

Quote:

I cannot really give you specific advice for your 80mm F5 as I don’t have one, so all I can say is that visually, on the Moon and Planets, the x5 PowerMate does not produce pleasing views through my Vixen 102mm F9 ED refractor. The magnified views are soft and do not reveal any further detail than the x2.5 PowerMate.

Well Dennis. That's very interesting info.. I guess the 5x Powermate might not be a good idea. Thanks for your help.

Quote:

Yeah I just got my 5x powermate, and do have to wind the focus inwards in order to focus an already focused eye-piece.

I visually used it once, and dare say I will not do so again... I bought it primarily for planetary imaging, and the views through it vs my 3x ED barlow were soft and somewhat lifeless in my 8" newt. however this could well have been due to the seeing conditions, which have been less than decent of late.

AlexN. Thanks for confirming that the focuser goes in with the 5x Powermate. I guess that confirms for me that it would not be a wise purchase for this application.

Thanks guys.

Regards,

Glob.

Prickly · #7 17-07-2008, 08:11 PM

Hi Glob 3.

What are you planning on using the barlow for?

My best barlow is my 1.8x televue barlow. Bought it years ago and it is a real ripper and now done approx 10yrs (better even by a smidge than the GSO 2x 2 inch barlow). Also it is 1.25 inch. I use it with my 4.8mm Nagler type 1 (was state of the art then!) - poor eye relief but what a great combo for sharpness (and light and afordable). You need the barlow to improve the eye relief with the 4.8mm. Ive had great planetary views with this barlow. My scope was then an 4 inch achromat by the way (light yellow filter also used) and great views of planets up to 275x.

I havent tried the 2.5x or 5x powermates but I've never looked through a bad televue either. Perhaps Im just a bit fussy with my barlows but remember they do last. Over 10yrs a good barlow pays off.

Cheers
David

Globular3 (Jeff) · #8 18-07-2008, 04:41 PM

Hello Prickly,

I was wanting to use the barlow for the moon, planets and resolving double stars with my 80mm f/5 refractor.

I read a great article that pneuman told me about in the thread entitled "Long Perng and Guan Sheng Eyepieces". Here is my reply with some points on barlows and powermates that might interest you. I've taken the liberty to BOLD the points of interest from my original reply.

Regards,

Glob.

Quote:

I'd probably steer clear of the GSO 5X -- I've heard from a couple of sources (online and offline) that it's not brilliant, with internal reflection that makes it essentially unusable for observing the Moon in particular. Here's one review that compares the 2.5X and 5X (it doesn't label them as GSO Barlows, but they definitely look like the GSO models from the photos):

http://www.astromart.com/articles/ar...article_id=600

Hello pneuman,

Thanks so much for the article from astromart.com.

(Link above in quote)

I agree with you, they do look like the GSO barlow lenses (also, they're made in Taiwan too!)

It has given me loads of help in the decision about the barlow (I'd buy the 2.5x now) as well as answering some questions. I'll summarise this below to help future readers.

1. The 5x barlow is no good for the moon otherwise, both barlows are good.

2. Barlow lenses work well within the low to mid eye relief range. They both increase the eye relief of the eyepiece used however, long eye relief eyepieces may be rendered unusable.

3. TELEVIEW POWERMATES are NOT barlow lenses even though they increase the magnification the same way as a barlow. THEY'RE DIFFERENT in that a POWERMATE WON'T CHANGE THE EYEPIECE EYE RELIEF. This is why POWERMATES CAN BE USED WITH LONG EYE RELIEF EYEPIECES.

4. Parfocal barlow means, focus the eyepiece WITHOUT the barlow. Remove the eyepiece, PUT IN THE BARLOW AND SAME EYEPIECE AS BEFORE, NO NEED TO RE-FOCUS.

All the best from,

Glob.

Prickly · #9 18-07-2008, 09:15 PM

Hi Glob3,

I must have missed that part. I havent read the article and when I click the link BTW it doesnt come up for some reason.

You are certainly right about the 5x being no good for the moon. Im just not that impressed with it at all for anything (other than 3 star aligning the Eq6) - so I may beg to differ on point 1 about the 5x being ok on other things. Maybe I just got unlucky with mine. My point is just that I hope the 2.5x GSO apo barlow is better than my 5x barlow.

My suggestion if you are not in a hurry is to try before you buy.

With a good refractor I've heard the max would be about 100x per inch (but probably less). Others can say 50x, but I've seen nice views through my 4 inch f10 achro at 275x certainly which is well more than that. I would look at your low power eyepiece and f ratios and work backwards from there. So from that if you were using a 5mm eyepiece with a theoretical max say of 320x (and probably a bit less than that) a 4x barlow would be more than heaps. You would get 200x with a 2.5 which sounds pretty reasonable.

Cheers,
David

Globular3 (Jeff) · #10 22-07-2008, 09:55 PM

Hello Prickly,

Sorry about the problem with the link. I simply copied and pasted the quoted link and didn't know I needed to use the hyperlink tool. The result was that the link wasn't complete. I fixed the link so it does work now. Have a look at the article, it's very interesting.

Thanks for the advice too. I was trying to work to a max magnification of 2.4x the lens diameter in mm. For the 80mm this would yield a max mag of 192. I've tried 200x with a 6mm (3x barlow) and 300x with a 4mm (3x barlow). Good seeing is needed with both but the 6mm combo seems better. The barlow is not the best so I'm hoping that the new one will improve the situation.

Regards,

Glob.