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BB Reviews the Bresser Messier AR-102L

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#51 precaud

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Posted 11 April 2019 - 09:41 AM

My Nikon curves the field in close-ups (DPAC patterns included).

 

Just in case you missed it, check post #31 for some cheap used digicam models that are excellent for DPAC, fringe testing, collimation pics, etc.



#52 Bomber Bob

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Posted 11 April 2019 - 07:41 PM

Second DPAC Test

 

Why does the retaining ring pop out?  The cell threads aren't continuous:  There 2 un-threaded areas approximately 1/4 the circumference, and 2 threaded areas -- each on the opposite side of its mate...

 

Bresser AR-102L S22 (Lens Cell Threads).jpg Bresser AR-102L S21 (Lens Elements).jpg

 

Note that the lens edges are blackened.  And, that there were NO alignment marks on those edges.  So before the test, I removed the lens, used my glass tool to make a slash on the flint's edge, colored it in with my red alcohol pen, then put it back in the cell.  Then, the gap ring (4.7mm thick), followed by the crown element.  I positioned the cell in my DPAC's holder so that my flint "anchor line" was at the 6 o'clock.  I set the retaining ring just loose enough that I could rotate the crown without moving the flint, checking the inside focus pattern along the way.  The following crummy Nikon photos are at IF (Inside Focus), AF (At Focus), and OF (Outside Focus) -- if you let your mouse hover over each photo, you'll see its file name.

 

Bresser AR-102 DPAC S01 (IF).jpg Bresser AR-102 DPAC S02 (AF).jpg Bresser AR-102 DPAC S03 (OF).jpg

 

The camera distorts bar width, and adds some curvature.  What I saw:  I got an excellent pattern IF, and marked it as seen in the photo (and made a permanent slash on the edge afterwards).  At focus, I saw a zone.  OF showed a bit of the center bar bloat, but much less than in the first test.  I also added sky-pointing arrows to both elements.  The alcohol pen marks came off easily.  After I thoroughly clean the cell, Humpty will be put back in its plastic Dumpty...

 

The lens fits so tightly in the cell that I can't tape the elements together at best alignment.  So, I'll position the crown, tighten that flimsy ring, and see how well it stays in place with routine use.

 

BIF:  I measured the focal length at 1365 +/- 5mm.


Edited by Bomber Bob, 11 April 2019 - 09:28 PM.

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#53 precaud

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Posted 11 April 2019 - 07:49 PM

The DPAC result is unimpressive...


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#54 Gabby76

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Posted 11 April 2019 - 08:03 PM

The lens fits so tightly in the cell that I can't tape the elements together at best alignment.  So, I'll position the crown, tighten that flimsy ring, and see how well it stays in place with routine use.

 

Interesting, mine was the opposite. The lenses had room to shift around and I had to shim them to keep the doublet centered. 



#55 Bomber Bob

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Posted 11 April 2019 - 08:42 PM

This cell has 4 divets / bumps that press in to hold the flint -- I think made by pressing a hot-point into the plastic from outside.  Obviously, it doesn't lock them in place, as I slid the entire lens out easily.

 

Both DPAC tests confirm my star tests.  My sky tests aren't complete, but what I've seen so far is nice for an economy refractor.  However, I've tested vintage cheap refractors where the maker took the time to test the lens, and mark the best alignment.  I guess this factory is saying it doesn't matter -- spin 'em any way you want.  It took me just a few minutes to find that best alignment, and with my homemade rig.

 

The lens is clean & reassembled -- and aligned.  IF we get a decent night this weekend, I'll repeat my first session, and look for any differences.

 

BIF:  The 4.7mm thick gap ring is aluminum, painted flat black.  It looked like plastic from the outside.  So, there are 5 metal cell parts -- counting the 4 tiny screws that hold it to the tube.


Edited by Bomber Bob, 11 April 2019 - 09:26 PM.

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#56 memento

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Posted 12 April 2019 - 08:39 AM

I never tried to change the adjustment of the two lens elements in any of my refractors. Always inserted them in the same relative position as they were before, sticking to the existing marks on the side.

Having said that I once received an old refractor where the lens elements were mixed up. As there were no marks left on the elements, I couldn't and didn't check rotational orientation when I corrected the fault. But it worked, good star test.

In other words, is it really necessary to rotate the lens elements against each other to some specific position to get the best performance, or is the Bresser approach correct – it does not matter, hence no alignment marks on the lenses?



#57 Bomber Bob

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Posted 12 April 2019 - 08:43 AM

Rotating / realigning the elements was a good thing for this refractor.  When I've had the time, I've checked it on other "known good" refractors, and most times the original edge marks are at the best position.


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#58 precaud

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Posted 12 April 2019 - 09:04 AM

 It took me just a few minutes to find that best alignment, and with my homemade rig.

 

I'm curious, how did you do this? What was the procedure and criteria?

 

I've only done 5, but I have yet to find a frac that could not be improved by re-optimizing the relative lens rotation.


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#59 peleuba

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Posted 12 April 2019 - 09:19 AM

I'm curious, how did you do this? What was the procedure and criteria?

 

+1

 

Its takes me a very long time, once I decide that I want to attempt to improve performance to, rotate/reassemble/test/photograph/rinse/repeat etc.  Even when doing an SCT corrector plate, where rotation will only improve the view a trivial amount, it takes me a long time.

 

Admittedly, I don't use DPAC to assess rotation errors, but rather, the star test using an indoor collimator.  I have found that rotational alignment is one "tool" to  address astigmatism which, for me, is and is easier to see with a star test.  DPAC helps me to determine if the elements are properly oriented - ie. not flipped or in backwards.


Edited by peleuba, 12 April 2019 - 09:25 AM.

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#60 Bomber Bob

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Posted 12 April 2019 - 09:56 AM

I'm curious, how did you do this? What was the procedure and criteria?

 

I've only done 5, but I have yet to find a frac that could not be improved by re-optimizing the relative lens rotation.

With my DPAC rig, as described in Post #52 -->  https://www.cloudyni...-3#entry9286563



#61 precaud

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Posted 12 April 2019 - 10:09 AM

With my DPAC rig, as described in Post #52 -->  https://www.cloudyni...-3#entry9286563

 

OK. Checking the inside focus pattern for what?

The problem I see with that approach is that it is blind to astigmatism, which from what I've seen is the most impacted by lens rotation.


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#62 Bomber Bob

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Posted 12 April 2019 - 11:10 AM

3 - 5 straight black bars, equal width, equal spacing for IF / OF pattern.  My better lenses have narrower darker bars than this lens, and no thickening of the central bar(s).  For most lenses, setting the pattern at 4 / 5 bars puts 2 on or close to the edge, and makes any curvature easier to see.

 

I did see a small zone at focus.  With my flint edge mark at 6 o'clock, it was at 2 o'clock.  If my pix were better, it would be obvious.  I didn't see any edge deformities.  I don't have any gear to measure lens curvature, but I've cleaned a ton of lenses over the years, and the R3 surface (flint's sky face) didn't look & feel like a match to the crown's R2, which I think it should with a Baker achromat.

 

Inside Focus:  Excellent star test & DPAC patterns with 3 - 5 bars.

Outside Focus:  Fuzzy star test & "bloated" DPAC bars.

At Focus:  Excellent resolution, very good contrast, micro-dot faint field stars, sharp limbs on Mars & the Moon, false color on the limbs.  So far, the views are what I'd expect from a good high F-ratio refractor.

 

It cost me about the same as my incomparable Dakin 4" F10, so that'll be the first scope I test it against.


Edited by Bomber Bob, 12 April 2019 - 06:23 PM.


#63 Bomber Bob

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Posted 12 April 2019 - 06:10 PM

Just finished assembling the Bresser.  Then, I cleaned & polished it -- looks sharp!  But, the dye in the tube ring's felt stained the paint.  Same thing happened with my APM 152ED, except it was fainter than this one.  It should come off with automotive rubbing compound -- with no damage to the paint.


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#64 Bomber Bob

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Posted 13 April 2019 - 11:26 AM

Rotating Focuser

 

After removing its lens cell for DPAC, I needed to re-collimate the Bresser, and I did that this morning with the rotating focuser at the index position (the Arrow aligned with the lock knob as delivered).  The lens cell has no "give" in it, but the focuser has 3 small grub screws that maintain pressure & position on it.  Before adjusting these, I examined how much "slop" in this feature affects collimation:

 

Bresser AR-102L S31 (Rotating Focuser).jpg Bresser AR-102L S32 (Rotating Focuser).jpg Bresser AR-102L S33 (Rotating Focuser).jpg

 

Rotating clockwise, the focuser as delivered does hurt collimation, and it varies quite a bit depending on where you lock it.

 

I used a small Allen wrench, and loosened / tightened these 3 screws to get the unit truly centered.  It feels more precise now, but the rotation still isn't predictable / reliable:

 

Bresser AR-102L S34 (Rotating Focuser).jpg Bresser AR-102L S35 (Rotating Focuser).jpg

 

The Bresser will be going up against my Dakin 4" F10.  Its focuser is fixed, but the focuser is attached to a base plate with 4 screws that can be loosened / tightened to make it square with the optical path:

 

Bresser AR-102L S36 (Rotating Focuser).jpg

 

I think the factory did a quick collimation check at the Index Position, and boxed it up.  I didn't see any degradations in the test sessions, but apparently the focuser gets looser with use.  On the plus side, this feature gives the owner the ability to nail collimation at the Index Position.  And, in use, if the view changes after rotation, unlock the knob, press the focuser flush against the flange, and re-tighten.  I'll test that in the next session.  From what I saw this morning, that restores collimation.


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#65 Bomber Bob

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Posted 13 April 2019 - 02:51 PM

Mirror Diagonal

 

How bad is the bundled mirror diagonal?  Pretty bad!  I imagine that it does OK with the bundled Bresser "Super Plossl" 25mm at 54x, but I bet just like the unit bundled with that ES FL AR-102, it's worse than useless.

 

I used the 6" flat from my DPAC rig (to boost pattern brightness), and both my laser collimators, so there a 3 pairs of pictures:  No diagonal, diagonal with laser perpendicular to light path, & diagonal parallel to the light path (IOW, I rotated the collimator 90* within the diagonal's holder):

 

Bresser AR-102L S41 (Mirror Diagonal).jpg Bresser AR-102L S42 (Mirror Diagonal).jpg Bresser AR-102L S43 (Mirror Diagonal).jpg Bresser AR-102L S44 (Mirror Diagonal).jpg Bresser AR-102L S45 (Mirror Diagonal).jpg Bresser AR-102L S46 (Mirror Diagonal).jpg

 

Collimation without the diagonal is spot on.  Use the diagonal, and collimation suffers.  And, the mirror itself is low quality.  It causes random scatter of the light.  IOW:  Chunk it if you buy this scope.  If the Bresser is like the ES, the 25mm eyepiece will be decent enough for low power, but we'll see.


Edited by Bomber Bob, 13 April 2019 - 02:56 PM.

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#66 Bomber Bob

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Posted 13 April 2019 - 03:41 PM

RECAP:  Is the Bresser AR-102L worth $250??

 

IMO, Yes.  Forget about the accessories.  I think folks who buy this scope are experienced amateurs, and already have better -- much better! -- diagonals & eyepieces.  Is there a market?  Well, I did some Google Shopping, and I couldn't find a 4" F8 - F15 achromatic refractor at $250.  Y'all can cross-check this, and please post if you find one.  There's the used market, but you take your chances on changes made / damages inflicted as the years / decades go by.  Who would be the Buyers?   I would, if I didn't already have a 4" high F-ratio refractor.  It's brand new, and it costs less than either my Dakin or my Edmund.  The lens is good, and produces an acceptable image.  The focuser is stout enough to carry heavy 2" accessories without slipping, and accurate enough to nail focus at high powers.  Like the other Bresser-branded tube rings that I own, these are perfect compared to the Orion, et. al rings -- and all were made in China.  

 

Here's my take on China-made gear:  It's the same situation as 50 years ago with Japan-made gear.  The Vendor has a retail price target, and the scope requirements / capabilities / features / quality are directly related to that target.  APM, Bresser, Celestron, etc. have to make a profit, and so do the actual scope makers in China.  So, do you go super cheap, and try to sell thousands of units; or, do you go middle tier, and sell fewer units; or, do you for top tier, and sell fewer units at a larger profit margin?

 

The AR-102L is a niche compromise unit.  The focal ratio is high enough to limit most false color, and keep the OTA size & weight low enough for middle weight mounts.  The lens is good enough quality to give decent views at high power.  The mechanics are good enough to support standard gear.  And the price is very reasonable for what you get.  IMHO:  I think Bresser may be ahead of the curve on the market, though, with the AR-102L.  Interest in short APO-ish ED doublets & triplets hasn't peaked yet.  I think it will.  At least for city dwellers who are mostly visual observers.  Altair may be in a similar situation, as they're "going long" at F11 with the Starwave Ascent 102ED APO.  Or, maybe Bresser & Altair have it right, or they're trying to build a new market...

 

How many refractor owners make DSO digital images on a regular basis?   If you don't, and you don't want to spend $1000 on an ED, the AR-102L is worth considering.  You can get a taste of classic refractor views without spending a fortune, or taking chances with a used / vintage 4" refractor.


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#67 Magnetic Field

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Posted 13 April 2019 - 04:10 PM

AR-102L on Goto 106 (3" EQ) + Unitron 142 Tripod

 

attachicon.gif Bresser AR-102L S15 (Goto Unitron).jpgattachicon.gif Bresser AR-102L S16 (Goto Unitron).jpg

 

This is as used last night.  As I posted, eyepiece height is comfortable for me in either of my lawn chairs.

 

Why would anyone want to buy a bulky 4" f/14 achromat when one could buy a 4" or 5" Maksutov with a similar f-ratio and with the additional goody of compactness and planetary sessions with no false colour?



#68 Bomber Bob

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Posted 13 April 2019 - 04:25 PM

Why would anyone want to buy a bulky 4" f/14 achromat when one could buy a 4" or 5" Maksutov with a similar f-ratio and with the additional goody of compactness and planetary sessions with no false colour?

As a Questar owner, I can think of a few reasons to buy an AR-102L versus a 4" Mak-Cass.  But first, how much is a brand-new China-made 4" MCT?

 

-- Temperature adaptation.  This frac adapts within minutes from cool house to hot outdoors -- MUCH faster than the typical MCT.  And, it transitions better throughout the night.

 

-- 2" Accessories.  How many 4" MCTs natively use 2" diagonals & eyepieces without vignetting?

 

-- Contrast & Resolution.  My $5000 Q has refractor-like C&R.  I can't imagine that a much cheaper 4" MCT with a central obstruction will beat this frac.  I'd have to see it myself.

 

Bulky?  In refractor terms, the AR-102L is a light-weight.   My 1980s Vixen Polaris will carry it, and these sell used for $150 or less -- right here on CN.  But yes, an MCT is a much more compact scope, and if space is at a minimum, it makes sense to buy one.

 

Sure, there's false color, but in refractor terms it's not excessive; and, from what I've seen, depends somewhat on the accessories as to how bothersome it is at the eyepiece.

 

Check my signature block.  I got all kinds of scopes, but I'm obviously a refractor fan, and this is the Refractor Forum, so my review is about apples to apples.


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#69 precaud

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Posted 13 April 2019 - 04:29 PM

Ni disrespect intended, but this comes off as a promotional effort.


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#70 Bomber Bob

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Posted 13 April 2019 - 04:39 PM

... this comes off as a promotional effort ...

 

Well, it's not.  No Bresser royalties coming to me from this review, and I certainly don't expect to make big bucks from selling this cheap frac.

 

I'm not rich, but dropping $300 on this scope didn't empty my wallet.  I've paid much more for what some folks on CN would call outright junk.  For example, I paid $300 for this:

 

Antique Brass 3IN Refractor ES01.jpg

 

That after my restoration became this:

 

Mogey 3 - Complete (Right Side) S01.jpg

 

But, I'm not gonna call this cheap frac junk.  I report what I see -- same as always.

 

In Case You Missed It, From Post #8:  "I parted it out:  Gave the mount to a new CN member who needed one, and gave the OTA to a young CN member who didn't have a "big" refractor."

 

My ES FL AR-102 review was no promotion -- I got no money from it.  I don't expect to make money from this review, either.


Edited by Bomber Bob, 14 April 2019 - 11:50 AM.

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#71 Magnetic Field

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Posted 13 April 2019 - 04:53 PM


 

-- Contrast & Resolution.  My $5000 Q has refractor-like C&R.  I can't imagine that a much cheaper 4" MCT with a central obstruction will beat this frac.  I'd have to see it myself.

 

 

False colour greatly reduces contrast.

 

And the resolution limit for a 4" Maksutov and 4" refractor are similar.

 

And then there is always the option to buy a 5" MCT.

 

 

My telescope is a Vicen VMC 110L. I once owned a Vixen 4" f/10 achromat. I would never ever considering buying an achromat again. Admittedly it was f/10 but the blue fringe around the planets, moon and Sun was not fun. There is no point buying an achromat.



#72 Bomber Bob

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Posted 13 April 2019 - 05:01 PM

My telescope is a Vicen VMC 110L.

 

Cool.  My largest aperture scope is a Vixen VMC200L, and it is a marvel -- but you gotta keep it collimated!

 

Some folks don't want to mess with that, or with the other issues compound scopes have.  They prefer refractors, hence this, the Refractor Forum.

 

Bresser sells a 100x1400 MCT for $260 -->  https://www.bresser....tical-Tube.html

 

I haven't tested it, but based on my experience, I seriously doubt it would stay as sharp at 80x per inch as the AR-102L does.  I love my Questar, but my Vixen FL80S whoops it on stars, diffuse nebulae, and galaxies.

 

Am I gonna ditch my APM 152ED, which is MUCH harder to deal with than the VMC200L?  No way!   Both are fine instruments, with very different traits & best object types, and I use them accordingly.


Edited by Bomber Bob, 13 April 2019 - 06:01 PM.

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#73 Bomber Bob

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Posted 13 April 2019 - 06:13 PM

The AR-102L's Competition

 

This review won't be through until I get to see and image Jupiter in 7/10 or better skies.  Since the Bresser will be compared with my Dakin F10 & Edmund F15, here's some samples from these two old fracs:

 

Dakin 4 - Jupiter (GRS) 20170609V04AT11.jpg Edmund 4 - Jupiter 20180806V07AS64S01.jpg


Edited by Bomber Bob, 13 April 2019 - 06:14 PM.

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#74 Steve Allison

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Posted 13 April 2019 - 06:29 PM

False colour greatly reduces contrast.

 

Depends on how much. Usually less than a big, fat central obstruction.

 

Had my Brandon 3 inch F/15 achro out last night to compare with my newly acquired 80mm F/7 fluorite doublet. Virtually identical performance. The apo was much shorter than than Brandon, but it was actually quite a bit heavier. Different strokes...

 

I have an optically excellent 4 inch SCT that is very sharp, but the 3 inch Brandon beats it hands down for contrast on objects like Jupiter.

 

The images I had in the vixen VMC110 I used to own were so soft that even my 50mm Zeiss threw up better images. The replacement unit I got from Vixen was no better. And with the large central obstruction and very thick, curved secondary support vanes contrast was pretty bad.

 

I would never, ever consider buying one of these units again. Not while I have my brace of long-focus achromats that produce bitingly sharp images with good contrast.



#75 Magnetic Field

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Posted 13 April 2019 - 07:06 PM



 

Depends on how much. Usually less than a big, fat central obstruction.

 

Had my Brandon 3 inch F/15 achro out last night to compare with my newly acquired 80mm F/7 fluorite doublet. Virtually identical performance. The apo was much shorter than than Brandon, but it was actually quite a bit heavier. Different strokes...

 

I have an optically excellent 4 inch SCT that is very sharp, but the 3 inch Brandon beats it hands down for contrast on objects like Jupiter.

 

The images I had in the vixen VMC110 I used to own were so soft that even my 50mm Zeiss threw up better images. The replacement unit I got from Vixen was no better. And with the large central obstruction and very thick, curved secondary support vanes contrast was pretty bad.

 

 

(What did you observe last night? The moon? Jupiter?)

 

Not only did you have 2 lemons.

 

I have to call you out on this and I don't think you gave much thought what you wrote. I always get annoyed when I read that unsubstantiated crap about central obstruction and contrast:

 

As if contrast is an absolute thing. And how did you observe "contrast"?  You did not evaluate it, but instead you have read somewhere on the web that central obstruction is the root of all evil and you fell for that trap.


Edited by Magnetic Field, 13 April 2019 - 07:07 PM.



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