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AP BARADV vs. GSO 2" Barlow

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#1 thecelloronin

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Posted 16 June 2021 - 11:46 PM

The AP BARADV is supposed to offer the best of all worlds: lightweight, optically excellent, and versatile in which magnifications you can get, from 1.8-2.5x. Numerous reports from trusted members suggest it indeed a nice piece of kit.

 

However, I'm a little unsure about it, primarily because I find the available product copy on the internet to be rather lacking in detail. Here's what we have:

  • Magnification factor 1.8x: @ 70mm back focus distance
  • Magnification factor 2.0x: @ 79mm back focus distance
  • Magnification factor 2.5x: @ 134mm back focus distance

Does the BARADV ship with three different-sized extension tubes, or is this BYOT (bring your own tube)? Or, are we meant to use a series of extension rings between the tube and the Barlow cell a la Baader Hyperion? In other words: What actually comes in the box? Is it just the Barlow element itself? If it does ship with a single extension tube, how long is it? And, how much does it all weigh? Got any pictures?

 

 

On the other hand, we have the GSO 2" Barlow which also gets pretty much universally good reviews. And just like the BARADV, the Barlow element unscrews and can be attached directly to an eyepiece. I also know you can vary the magnification by using different length extension tubes.

 

The BARADV is $250 while the GSO is $60, yet the seem to offer almost identical benefits. What am I missing here? How do the two compare, and how do they contrast?


Edited by thecelloronin, 17 June 2021 - 12:02 AM.


#2 areyoukiddingme

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Posted 17 June 2021 - 12:11 AM

In my experience, screwing the barlow directly to an eyepiece does not yeild acceptable results (edges with Leica zoom look very astigmatic).

 

I find that inserting many eyepieces directly gives 1.8, or even less magnification. I only start approaching 2x when I use a hi-hat televue adapter. So even to get to 2x means using an a adapter. I've never bothered to attempt to get more power, as it would mean a rather long stack with extensions.

 

The Nikon 1.6x zoom gets a whole lot more use for me. It gives 1.82x when I use it with the Leica and APM adapter, so it does the same as the BARADV, and with a whole lot less weight and I can't tell the difference.

 

I also have a Zhummel 2" 2x barlow, and it is excellent. I assume it's the same as the GSO. It would be very difficult to tell the difference from the A-P.


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#3 25585

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Posted 17 June 2021 - 12:48 AM

Antares make a 2" 1.6× Barlow which performs well.

 

My AP BARADV is as good as my Zeiss Abbe optically, the latter is 1.25" fit. I have not tested the AP for exact magnification.

 

GSO 2x works with the TV PBI lens.



#4 MarMax

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Posted 17 June 2021 - 12:56 AM

I just bought the AP BARADV and this is the only photo I have handy. I'm using the barlow nose piece ahead of a ZWO ADC. The nose piece is 24mm, the rest of the BARADV is 88mm with a 10mm nose where the barlow nose threads in. There is a shoulder on the inside of the 2" EP adapter that is 72mm below the top edge.

 

gallery_332504_16866_58852.jpg

 

EDITED to ask where you got the information on backspacing. This is what is shown on the AP site:

 

"Changing the spacing distance will change the magnification of the Barlow (90 mm back spacing is ideal, yielding 2.0x magnification). The “sweet spot" of the flatter field is between 1.8x and 2.5x."

 

The missing info is the "where" the backspacing is measured from. The link on the AP site to the chart does not really make any sense to me. It's called an Advanced Convertible Photo-Visual Barlow (BARDEV) yet the chart refers to a BARCON. I'd just assume that BARCON = BARADV but the chart does not show 2x at 90mm so what's up with that?


Edited by MarMax, 17 June 2021 - 01:11 AM.

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#5 sixela

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Posted 17 June 2021 - 03:08 AM

I'm curious -- my BarAdv doesn't have standard threads at the telescope end of the barlow -- it's singificantly more narrow than M42 (T2). How do you even connect it to the diagonal?


Edited by sixela, 17 June 2021 - 03:22 AM.

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#6 dUbeni

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Posted 17 June 2021 - 06:41 AM

I'm curious -- my BarAdv doesn't have standard threads at the telescope end of the barlow -- it's singificantly more narrow than M42 (T2). How do you even connect it to the diagonal?

Hi sixela, that is strange indeed, mine has both T2 and M48 male threads and I can attach it to the telescope end of a Baader T2 prism or the Baader 2" ClickLock.

 

My measured focal lengths using the BARADV in front of Baader T2 Zeiss prism are 2.59x and with a 35mm extension tube 2.95x. The telescope used was a Vixen ED80S f/9.

 

 

Does the BARADV ship with three different-sized extension tubes, or is this BYOT (bring your own tube)? Or, are we meant to use a series of extension rings between the tube and the Barlow cell a la Baader Hyperion? In other words: What actually comes in the box? Is it just the Barlow element itself? If it does ship with a single extension tube, how long is it? And, how much does it all weigh? Got any pictures?

The BARADV doesn't come with extension tubes, the M48 extension tubes are more useful for visual since they match a 2" barrel.

 

CS

Bernardo



#7 thecelloronin

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Posted 17 June 2021 - 10:15 AM

Okay, just so I'm sure I understand...

 

Here's the picture of the BARADV on AP's website

 

Screen Shot 2021-06-17 at 11.04.42.jpg

 

And Teleskop-express:

 

Screen Shot 2021-06-17 at 11.05.01.jpg

 

Two different extension tubes are pictured. But, y'all are saying neither of them come in the box. Buying the BARADV, thus, is just buying the Barlow lens element, correct?

 

EDIT: the second image matches what I see in MarMax's photo. So, it does ship with an extension tube? 


Edited by thecelloronin, 17 June 2021 - 10:38 AM.


#8 MarMax

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Posted 17 June 2021 - 10:47 AM

I'm curious -- my BarAdv doesn't have standard threads at the telescope end of the barlow -- it's singificantly more narrow than M42 (T2). How do you even connect it to the diagonal?

I use the ZWO M42 to M48 adapter ring.

 

Okay, just so I'm sure I understand...

 

Here's the picture of the BARADV on AP's website

 

attachicon.gifScreen Shot 2021-06-17 at 11.04.42.jpg

 

And Teleskop-express:

 

attachicon.gifScreen Shot 2021-06-17 at 11.05.01.jpg

 

Two different extension tubes are pictured. But, y'all are saying neither of them come in the box. Buying the BARADV, thus, is just buying the Barlow lens element, correct?

 

EDIT: the second image matches what I see in MarMax's photo. So, it does ship with an extension tube? 

The 2nd image is correct. The only pieces (2) that came with mine are shown the photo. I believe the adjust ability is through using the nose (barlow) in different direct configurations. It is very handy having the male T2 and M48 threads on one side and M48 female on the other. But is it worth $250, that's the question I don't have an answer for.


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#9 25585

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Posted 17 June 2021 - 10:56 AM

I would go by the AP site. Other sites may use older stock photos. 

 

 

https://www.astro-physics.com/baradv


Edited by 25585, 17 June 2021 - 11:18 AM.


#10 thecelloronin

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Posted 17 June 2021 - 11:03 AM

I would go by the AP site. Other sites may use older stock photos. The BARADV's predecessor was called a BARCON, older photos might be of that.

In this case, it seems AP's site is what's outdated.

 

Antares make a 2" 1.6× Barlow which performs well.

Do you notice a difference in optical quality between the Antares and the BARADV? If so, how would you describe the difference?

 

I use the ZWO M42 to M48 adapter ring.

 

The 2nd image is correct. The only pieces (2) that came with mine are shown the photo. I believe the adjust ability is through using the nose (barlow) in different direct configurations. It is very handy having the male T2 and M48 threads on one side and M48 female on the other. But is it worth $250, that's the question I don't have an answer for.

Okay, cool. So they give you a tube, and leave it up to you to supply your own alternative tubes should you want to change magnifications. Thanks for confirming! While we're at it, could you possibly measure the overall length of the tube itself for me, and weigh it all put together with the Barlow lens? These are numbers which AP frustratingly doesn't provide...


Edited by thecelloronin, 17 June 2021 - 11:04 AM.


#11 thecelloronin

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Posted 17 June 2021 - 11:11 AM

In my experience, screwing the barlow directly to an eyepiece does not yeild acceptable results (edges with Leica zoom look very astigmatic).

 

I also have a Zhummel 2" 2x barlow, and it is excellent. I assume it's the same as the GSO. It would be very difficult to tell the difference from the A-P.

I've noticed significant softening of the field stop screwing my generic Chinese Barlow into the end of my Nagler 22. I always chalked it up to it being a low-quality Barlow, but your first statement has me second guessing that.

 

As to your second statement about the Zhummel/GSO, I'm curious as to why someone would buy the BARADV if the GSO is optically about as good. Moreover, it seems the mechanism by which you can vary the magnification (using different extension tubes, hi-hat adapters, or extension rings) are not unique to the BARADV.

 

Could it be possible that where AP states their Barlow's "sweet spot" is between 1.8x and 2.5x, the GSO has a narrower range of variable sweet spot magnifications? I'm trying to understand the $190 price difference. Not that I'm afraid to pay for quality, but if all things are basically equal for visual observing, it seems the GSO is the no-brainer. 

 

I'm not skeptical of AP or the BARADV, but the benefits of paying that premium aren't being well communicated.



#12 25585

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Posted 17 June 2021 - 11:25 AM

Not much difference between my GSP 2x & Antares. The AP is slightly better for higher magnifications. Light transmission is very good with the AP, I use it with my ES92s and it holds their weight firmly.


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#13 MarMax

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Posted 17 June 2021 - 11:29 AM

trim

could you possibly measure the overall length of the tube itself for me, and weigh it all put together with the Barlow lens? These are numbers which AP frustratingly doesn't provide...

Here's a couple more pics for you. The total weight is 10oz (284 g) based on my cheap postal scale. The overall length is just 88 + 24 = 112mm. 

 

gallery_332504_16866_260220.jpg

 

Just the nose so you can see the M42 and M48 threads.

gallery_332504_16866_48436.jpg


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#14 thecelloronin

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Posted 17 June 2021 - 11:38 AM

Awesome, thanks guys. 

 

25585, around what magnification would you say the BARADV pulls slightly ahead of the cheaper Barlows?

 

 

MarMax, just making sure: the extension tube is 88mm, and the lens cell is 24mm? 



#15 MarMax

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Posted 17 June 2021 - 11:48 AM

trim

MarMax, just making sure: the extension tube is 88mm, and the lens cell is 24mm? 

Yes, that is correct. Total length = 112 with the 88mm extension tube and 24mm nose. The 24mm is shoulder to end.

 

And on the inside of the extension tube the "shoulder" is 72mm below the top. Not sure what that matters since there is no EP with a nose that long. I guess it's just to protect the barlow cell in case you dropped a 2" extension tube inside.

 

I'm using binoviewers so keeping the weight down is important. The only part I'll ever use is the barlow nose piece.

 

The main reason I bought it is because it was in stock and everything else I checked on was on back order.

 

I've wanted to buy a new pair of 13T6's for six months now and they are nowhere to be found.

 

EDITED to add that the graph from AP shows the BARCON (BARADV) is 2x at 125mm backfocus and 2.5x at 190mm backfocus. Has anyone confirmed this?

 

Using the BARADV followed by the ADC then the CZAS viewer is about 200mm so I've assumed I'm at about 2.5x.


Edited by MarMax, 17 June 2021 - 11:53 AM.


#16 25585

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Posted 17 June 2021 - 11:48 AM

Awesome, thanks guys. 

 

25585, around what magnification would you say the BARADV pulls slightly ahead of the cheaper Barlows?

 

 

MarMax, just making sure: the extension tube is 88mm, and the lens cell is 24mm? 

Can't say, but I notice more using it looking at the Moon. No loss of image anywhere & a flatter field with the AP. Of my 2", only the Takahashi dedicated 1.5x & 1.6 extenders for their refractors better the AP. 

 

The AP is good value and its variability makes mine a keeper with my Antares, buy both!  https://www.rotherva...twist-lock.html

 

https://stargazerslo...s-16x-2-barlow/


Edited by 25585, 17 June 2021 - 11:51 AM.


#17 MarMax

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Posted 17 June 2021 - 12:00 PM

I just read up on the Antares 1.6x and it's designed for 55mm of backfocus. Just in case anyone is using a binoviewer like the Baader MBII at 120mm backfocus or CZAS at 148mm. It may not be a good option unless it has a wide usable range like the BARADV.

 

Is there a graph of the Antares 1.6x that shows this?



#18 areyoukiddingme

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Posted 17 June 2021 - 03:14 PM

Seems there are different housings for the A-P.

 

I just measured mine at 3 and 7/8 inches, or 98.4mm from top to the bottom of the barlow.

 

And I just compared the magnification factors for the A-P and GSO using the 22 Nagler fully inserted.

 

For the A-P I get 1.81x, whereas for the GSO I get 2.14x.

 

Then when I swap the housings, the A-P in the GSO body, I get 1.95x, and the GSO in the A-P housing I get 2.08x.

 

While I think the A-P is the better quality barlow, it would take some very careful back-and-forth to see the difference. If you just want to be sure that you have an excellent quality barlow, then go for the A-P.

 

But also bear in mind that the A-P also does not come with a 1.25" adapter, just a plastic plug.

 

As for screwing the barlow directly to the bottom of an eyepiece, I find the results just too objectionable with any eyepiece I have tried that with. The edges become astigmatic and there's a (seeming) vignetting effect where the field stop becomes difficult to locate. The A-P would also appear to need an adatper to be able to do this in any case. The GSO can be screwed directly to the bottom of the 22 Nagler.

 

I've found myself gravitating much more in favor of 1.25" accessories to get magnifications higher and just leave the 2" stuff alone. For me it's the 1.6x Nikon barlow and the 2.5x Powermate.

 

IMG_0774.JPG



#19 sixela

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Posted 17 June 2021 - 03:19 PM

As for screwing the barlow directly to the bottom of an eyepiece, I find the results just too objectionable with any eyepiece I have tried that with.

 

It works, but only if you add so many extenders that you're back at a barlow factor of at least 1.8x. Since I bought it mainly because of the long focal length, which would have allowed lower factors if it could be used without adding those extenders, that barlow is a bit pointless for me (as a screw-on barlow the Baader VIP handsomely beats it).

I guess I'll be parting with it, even though indeed with factors between 1.8 and 2.5 it's really good.


Edited by sixela, 17 June 2021 - 03:20 PM.


#20 steffenyount

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Posted 17 June 2021 - 05:22 PM

A while back, I found that the "system chart for configurations" link on of the BARADV page, documents two examples for "flat field spacing":
https://www.astro-ph..._acc/baradv.pdf

 

From this I calculated the "flat field" back focus of both configurations at:

 

{parts: 15 (A3703), 14 (67RLEOS), 7 (Canon EOS)}
12.7mm + 34.4mm + 44mm = 91.1mm

 

{parts: 8 (AP16T), 16 (BP25C), 6 (T-Ring), 7 (Canon EOS)}
28.7mm + 7.5mm + (14.2mm - 3.2mm) + 44mm = 91.2mm

 

That puts their ideal spacing closer to 91.1mm (rather than 90mm)...

 

My BARADV is assembled with the following spacers, leaving ~55mm of back focus for use with my ASI cameras from the last M48 thread:

 

{parts: (M48 16.5mm extension), (M48 1mm spacer ring), (M48 10mm extension), (Stellarvue SFA-M63M48F48-003), (ZWO ASI camera)}
16.5mm + 1mm + 10mm + 8.6mm + 55mm = 91.1mm

 

My BARADV

Edited by steffenyount, 17 June 2021 - 05:30 PM.


#21 MarMax

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Posted 17 June 2021 - 06:32 PM

EDITED since this is probably wrong. See the Post #24 for what is probably correct.

 

The "sweet spot" for the BARADV is supposed to be between 1.8x and 2.5x. Looking at the "from rear flange" graph I come up with the following:

 

Magnification = (BackSpacing x 0.0077) + 1.15

 

For 1.8x the backspacing is 84mm and for 2.5x the backspacing is 175mm. Running the formula for 91mm gives a magnification of 1.85x. And 2x is more like 110mm.


Edited by MarMax, 17 June 2021 - 08:37 PM.


#22 dUbeni

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Posted 17 June 2021 - 06:49 PM

I got mine six years ago from Teleskop Service and it looks the the first photo you've shown (from AP web site)

 

21 weight lift IMG 7835
Here is attached to the prism via T2 thread (1.82x)
 
20 A gorgeous EP

Here the whole BARADV is inserted like a regular barlow before the prism (2.59x)

 

Edit: The way I read the info on AP website is that those distances apply to astro-photography, in other words the distances to the chip and their magnifications.

I really like it a lot.

 

CS

Bernardo


Edited by dUbeni, 17 June 2021 - 06:55 PM.


#23 steffenyount

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Posted 17 June 2021 - 06:56 PM

... yet the chart refers to a BARCON. I'd just assume that BARCON = BARADV but the chart does not show 2x at 90mm so what's up with that?

The BARCON was a predecessor to the BARADV (it's supposed to have improved field flatness).

I assume that's why those BARCON charts don't show 2x at 90mm.

 

FYI, the barlow system chart suggests: (BARADV: 1.8x = 70mm, 2x = 90mm, 2.5x = 134mm)
https://www.astro-ph...ystem-chart.pdf
 

I chose the BARADV for its flat field abilities...


Edited by steffenyount, 17 June 2021 - 07:05 PM.

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#24 MarMax

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Posted 17 June 2021 - 08:35 PM

The BARCON was a predecessor to the BARADV (it's supposed to have improved field flatness).

I assume that's why those BARCON charts don't show 2x at 90mm.

 

FYI, the barlow system chart suggests: (BARADV: 1.8x = 70mm, 2x = 90mm, 2.5x = 134mm)
https://www.astro-ph...ystem-chart.pdf
 

I chose the BARADV for its flat field abilities...

Yep, I'd trust the system chart you linked since it says BARADV. Good to know and the hopefully the correct formula is more like:

 

Magnification = (0.011 x BackFocus) + 1.03

 

I EDITED my Post #21 since that info is probably wrong.


Edited by MarMax, 17 June 2021 - 08:39 PM.

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#25 thecelloronin

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Posted 18 June 2021 - 03:11 AM

It works, but only if you add so many extenders that you're back at a barlow factor of at least 1.8x. Since I bought it mainly because of the long focal length, which would have allowed lower factors if it could be used without adding those extenders, that barlow is a bit pointless for me (as a screw-on barlow the Baader VIP handsomely beats it).

I guess I'll be parting with it, even though indeed with factors between 1.8 and 2.5 it's really good.


Well let me know if you do decide to chuck the BARADV!


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