High quality Barlow vs decent quality eyepieces.

[awestruck]

Hey everyone. Although ive read that at similar quality levels fixed focal length eyepieces beat out Barlows. My question is at a high level of quality such as a televue barlow, would the quality compare with specialised eyepieces for slightly lower end models such as celestron luminos or meade hd-60. Looking for best quality and highest diversity of magnification options on a budget.

[swamp thing]

Hi

I Use the TV 2" x2 power mate. Brilliant piece of kit. 

I'm so impressed with it I build my eyepiece collections around it. As you say its way cheaper and IMHO just as good as any solo eyepiece. 

[damnut]

The powermate as above is excellent, if you can afford one buy it. Else a decent ed barlow will cost around £40 s\h... Though I have a barlow I prefer to use without. And before other comments the Powermate is not a barlow.

[Alien 13]

I have wondered if a very good barlow actually improves the performance of lesser eyepieces in a fast scope by increasing the effective F ratio?

Alan

[damnut]

Hi Alan,

You are spot on, by increasing the effective focal length of a fast to medium focal ratio telescope, the diverging lens optics of a Barlow give inexpensive or moderately priced eyepieces a slower-converging and easier-to-handle light cone to deal with. This results in lower astigmatism and better color correction at the edge of the eyepiece field.
 

[nicoscy]

Alan,

I think it is actually the opposite as an increase in magnification will also amplify the aberrations in eyepieces not fully corrected...

[swamp thing]

Alan,

I think it is actually the opposite as an increase in magnification will also amplify the aberrations in eyepieces not fully corrected...

Err no.

Barlows will correct some aberrations as they increase focal length. They can actually help some eyepieces perform better.

Here have a read of this

[Moonshane]

another aspect of barlows (but not powermates) is that they increase the eye relief. this can help with some eyepieces (short eye relief) and hinder with some (those with already long eye relief).

[damnut]

Absolutely, hence longer focal length scopes are more forgiving with lesser quality ep's. The Powermate keeps the original exit pupil.

[nicoscy]

Err no.

Barlows will correct some aberrations as they increase focal length. They can actually help some eyepieces perform better.

Here have a read of this

Thanks for the link. Must do some more investigation. Actually I avoid barlows and only use OCA elements in my binoviewer. I prefer to have more eyepieces around 

[awestruck]

So wven though ive seen that barlows have a bad reputation. The high quality models such as the televue powermate are exempted just due to precise manufacturing/optics quality etc?

[awestruck]

As far as i can tell from a theoretical stand point a barlow shouldnt take away from image quality as long as light transmission is good and there are no defects in its manufacturing. Hence my confusion regarding everyones distaste.

[John]

From a theoretical standpoint any additional glass / air-to-glass surfaces are going to have some impact to light transmission and possibly light scatter. Some barlow / telextender designs have got that controlled to the point where it's not noticable though through the use of clever optical design, top quality materials and careful manufacture and testing.

[Charic]

On a budget, a Barlow makes sense to me. Theres also more glass in the optical train, if thats any worry. Paying premium will assist light transfer, with the better glass/coatings ?

I have a range of EP focal lengths to choose from, and yet still use 'part' of my Barlow. I just use the lens without the barrel, giving a lower Barlow factor. I dont notice any degredation or colour shift, , only the change in magnification.

[alan potts]

I used to have a 2 inch X2 Powermate and they are without doubt an excellent piece of equipment, I have used barlows but prefer the former. I do not own one now as it did not get the use it deserved, I used to make 5mm and 4mm Ethos eyepieces with it and it worked unbelieveably well, the only problem was the eyepiece was rather long, on my M/N 190mm I was worried the focuser would snap off .

Alan

[Pig]

I believe the Baader VIP Barlow is quite a good option and if your on a budget the Tal are excellent.

[awestruck]

Thanks to everyone for the replies and input. I have to decide whether the powermate is within my price range. The 1.25" models are well within me budget but having the 2 inch capabilty is sort of the point. Being able to buy high quality low power EPs and still getting high power options. Might have to hold off a while and save up. Knowing very little about barlows (and their difference with the powermate) are there any repercussions wuth using super widefield eyepieces. Such as 82 degree luminos or meade models.

[niallk]

FWIW I find my 2.5x Powermate great... But then I have a very limited EP collection to comment much further. I can say that it is outstanding compared to my cheap barlow... no discernable impact other than magnification.

I now also use my PM instead of a GPC when binoviewing with my 15" to overcome focusser travel issues. I end up with ~2.1x mag factor.

[SpaceWalker]

Thanks to everyone for the replies and input. I have to decide whether the powermate is within my price range. The 1.25" models are well within me budget but having the 2 inch capabilty is sort of the point. Being able to buy high quality low power EPs and still getting high power options. Might have to hold off a while and save up. Knowing very little about barlows (and their difference with the powermate) are there any repercussions wuth using super widefield eyepieces. Such as 82 degree luminos or meade models.

Why spending $$$ on the TV Powermate when you can save and get the same quality with the ES Focal Extender ? Read this thread on CN, the ES FE performs equally well and it also is a telecentric as the Powermate. I have several barlows but almost exclusively use the 1.25" 2x Meade TeleXtender, which is a rebrand of the ES FE. It works so good that I practically never notice if I have some extra glass in optical train. The only situation when you might see *some* (probably a hair) difference vs. fixed FL eyepiece is when you observing threshold objects/features which is infrequent, IMO. For that kind of situations I have few fixed FL Plossls, Orthos, RKEs etc (miserable eye relief!  ), but for general viewing with wide angle eyepieces my TeleXtender works perfect.

>are there any repercussions wuth using super widefield eyepieces

Longer FL (14mm+) 82*AFOV eyepieces show vignetting when used with a regular telenegative barlow. No any problem when used with the telecentric. This is my experience but it's well known though.

As for the 2" format think about weight and size. These Barlows are bulky and heavy and usually create balance problems. I have the 2" Barlow and hate it because of that. If you have a chance, try a  2" Barlow before you buy otherwise you can be disappointed. But maybe not, it's just a matter of taste.

[Moonshane]

one reason I choose different eyepieces is that a (1.6 x) 2" barlow with a 13mm Ethos is somewhat of a baseball bat compared with a 9mm ortho equating to the same focal length

[John]

Thats a well illustrated point Shane

Baseball bat is a good descriptive term. The ES Focal Extender and the Meade TeleXtender are good alternatives to Powermates but still add that length and weight:

[damnut]

I'm more of a red wine man..

[Pig]

Half a bottle !!!!!

[alan potts]

Why spending $$$ on the TV Powermate when you can save and get the same quality with the ES Focal Extender ? Read this thread on CN, the ES FE performs equally well and it also is a telecentric as the Powermate. I have several barlows but almost exclusively use the 1.25" 2x Meade TeleXtender, which is a rebrand of the ES FE. It works so good that I practically never notice if I have some extra glass in optical train. The only situation when you might see *some* (probably a hair) difference vs. fixed FL eyepiece is when you observing threshold objects/features which is infrequent, IMO. For that kind of situations I have few fixed FL Plossls, Orthos, RKEs etc (miserable eye relief!  ), but for general viewing with wide angle eyepieces my TeleXtender works perfect.

>are there any repercussions wuth using super widefield eyepieces

Longer FL (14mm+) 82*AFOV eyepieces show vignetting when used with a regular telenegative barlow. No any problem when used with the telecentric. This is my experience but it's well known though.

As for the 2" format think about weight and size. These Barlows are bulky and heavy and usually create balance problems. I have the 2" Barlow and hate it because of that. If you have a chance, try a  2" Barlow before you buy otherwise you can be disappointed. But maybe not, it's just a matter of taste.

Yes this would be good to, I sort of forgot about these which are basically clones of the TV Powermater. I used a Meade Tele-extender about 5 years ago which is the same as the ExSc model, both having been made at the same factory. I believe Bresser now market the old Meade model but which ever you buy they are the same thing in different trousers and boxes.

The Powermates do not vignette any of my Ethos eyepieces so they will for sure not bother a 82 degree or less. I imagine the Tele-extender will do the same.

I didn't read the complete thread so sorry for not picking up on this point, I thought someone would have said.

Alan 

[michael.h.f.wilkinson]

I have two Meade Series 5000 TeleXtenders (2x and 3x), and a TeleVue PoweMate (2.5x). It is not possible for me to tell them apart except for the difference in magnification. I use them almost exclusively for planetary and lunar imaging. I have used them in conjunction with EPs, but there are two reasons I do not regularly do this: (i) I have by now got a pretty complete (OK, nobody believes that ) EP collection, so can do without tele-centrics or Barlows, and (ii) I do not like the extra faffing around switching EP and  Barlow (or tele-centric lens). Having said that, they are a cost effective way to extend your range of EPs.