520 replies to this topic

[John R.]

It may of been because I was using a Baader Morpheus when testing for infinity and therefore was causing more inward focus.

Sounds like you got a good specimen of the 70mm F5.7. Perhaps you also removed any edge problems by reducing it to 65mm (F6).

 

Best Leah

I often do surgery on my cheap refractors, and had removed as much of the drawtube as I could get away with. After fixing up my friends 50x600 Tasco I have kept an eye out for one but surprisingly haven’t seen any at thrift stores or garage sales. 
I did finally get a Galileoscope off of ebay. A 50x500mm cemented doublet that measures 47.5mm clear aperture, it also presents a very sharp image right to the limit of it’s aperture. 
Here it is, considerably modified from its original configuration.

 

[Princess Leah]

I often do surgery on my cheap refractors, and had removed as much of the drawtube as I could get away with. After fixing up my friends 50x600 Tasco I have kept an eye out for one but surprisingly haven’t seen any at thrift stores or garage sales. 
I did finally get a Galileoscope off of ebay. A 50x500mm cemented doublet that measures 47.5mm clear aperture, it also presents a very sharp image right to the limit of it’s aperture. 
Here it is, considerably modified from its original configuration.

 

IMG_0485.jpeg

Looks great. What kind of mount is that? I'm struggling to find a mount for these small refractors.

[John R.]

That AZ mount is a homemade contraption inspired by Mark Mittlesteadt’s version. 
Two SkyWatcher slow motion pucks + aluminum brackets and a vixen clamp from an Orion one armed dob. All on a salvage tripod, although it has a standard 1/4-20 tap to fit most any photo tripod. 
I agree it is hard to find a reasonable small and lightweight mount for small refractors that doesn’t cost $300 to $400. 
From what I have read here the Svbony SV225 can be, with a bit of fine tuning, a solid AZ mount head. But I have no direct experience with it. 
 

Edited by John R., 16 April 2025 - 01:32 PM.

[Princess Leah]

Yes, the Svbony works great. Just quite heavy for a 50mm.

Thanks Leah.

[Granite Glasser]

Chromatic Aberration is only ONE component of the image formed by a telescope's objective.

I, apparently, am not that sensitive to it and a little bit doesn't seem to get noticed by me.

On the other hand, there other a number of OTHER characteristics of a refractor's objective that really DO make a difference in the viewing experience.  

Lens figuring, lens polish, coatings, the overall match between the individual lens elements, the degree of correction (over/under etc.),.... all of THESE aspects GREATLY affect the sharpness, contrast, field curvature or flatness, and other discernable attributes of the image which, to me, are far more important to the viewing experience than a tiny bit of CA. 

 

I'll take a finely engineered, well configured, superbly polished, well matched, flat field Achromat with everything done right over a lesser quality FPL-53 (or whatever) objective lens ANY DAY!

 

I expect ALL aspects of an achromatic objective lens to generate the best possible image and CA is only but one consideration and it is certainly NOT the most important one on my list.   

 

PEACE, 

Bobby 

Kalamazoo, MI 

[John Huntley]

Chromatic Aberration is only ONE component of the image formed by a telescope's objective.

I, apparently, am not that sensitive to it and a little bit doesn't seem to get noticed by me.

On the other hand, there other a number of OTHER characteristics of a refractor's objective that really DO make a difference in the viewing experience.  

Lens figuring, lens polish, coatings, the overall match between the individual lens elements, the degree of correction (over/under etc.),.... all of THESE aspects GREATLY affect the sharpness, contrast, field curvature or flatness, and other discernable attributes of the image which, to me, are far more important to the viewing experience than a tiny bit of CA. 

 

I'll take a finely engineered, well configured, superbly polished, well matched, flat field Achromat with everything done right over a lesser quality FPL-53 (or whatever) objective lens ANY DAY!

 

I expect ALL aspects of an achromatic objective lens to generate the best possible image and CA is only but one consideration and it is certainly NOT the most important one on my list.   

 

PEACE, 

Bobby 

Kalamazoo, MI 

I generally agree with that.

 

It's getting quite hard to find well configured, polished, matched etc, etc achromats though.

 

I've found that objectives that use expensive glass types (eg: FPL-53) seem to be better figured, polished, matched etc. So you get the benefit of that plus the better control of false colour plus they usually achieve that at faster focal ratios so the resulting instrument is easier, and less expensive, to mount effectively.

[John R.]

I generally agree with that.

 

It's getting quite hard to find well configured, polished, matched etc, etc achromats though.

 

I've found that objectives that use expensive glass types (eg: FPL-53) seem to be better figured, polished, matched etc. So you get the benefit of that plus the better control of false colour plus they usually achieve that at faster focal ratios so the resulting instrument is easier, and less expensive, to mount effectively.

These days most achromats are low end, built to sell for the lowest price. This seems to be true even for apertures larger than the ubiquitous 60mm x 700mm  ‘hobby killer’. 
In another thread the OP is wondering why he cannot find a 70mm achromat with a metal focusing mechanism.
Perhaps this is why there is a thriving used market in older, made in Japan

refractors. Generally better built focusing mounts, unfortunately most were .965 visual backs. 
I have a Towa 339 (80mm x 1200mm f15) that has beautiful construction and even a collimation lens cell. It was .965 but after unscrewing that, the draw tube has an OD of 1.26 inch, so it was relatively simple to clearance a 1.25 ID aluminum tube and slip it over the draw tube, leaving 2 inches depth. 

[Gonariu]

Last September I tried a friend's Bresser Skylux 60/700, I have to say that the optics were good but the finder and the tripod-mount assembly were clearly terrible and should be thrown away. The Konus 60/700 I had as a boy and the vintage Bresser 60/900, bought by me a couple of years ago, are decidedly superior in terms of the finder and mount.

Edited by Gonariu, 18 April 2025 - 05:07 PM.

[Tropobob]

I recently purchased a 90x900mm Skywatcher refractor on an AZ3-R mount.  This 90mm scope has a very interesting feature. 

 

The little cap on top of the aperture cap gives a 60mm option, which makes it much larger than the normal gap of approximately 42mm. When stopped down to this lower aperture, false color disappears, as this gives me a 60mm F15 option that easily meets the Conrady Standard.  It works well. Looking at an unsteady, setting Jupiter makes the image much more appealing to the eye. I find it helpful when looking at wide double stars that only need up to about 60x.  Furthermore, the small amount of false color that was visible during daytime viewing just completely disappeared.    

 

It would be nice if manufactures provided caps like this:  A cap that gives an option smaller aperture which is approximately 2/3rds of the original.  On doing the maths, a 150mm F8, stopped down to 100mm gives a scope that is a 100mm F12 which meets the Sidwick standard.   A100mm F5, stopped down to 65mm only just fails to also meet the Sidwick's criteria.   

 

Yeah, one can devise your own DIY way of stopping down aperture, but few bother. It is much better to have the device provided. 

 

 

[Princess Leah]

Last September I tried a friend's Bresser Skylux 60/700, I have to say that the optics were good but the finder and the tripod-mount assembly were clearly terrible and should be thrown away. The Konus 60/700 I had as a boy and the vintage Bresser 60/900, bought by me a couple of years ago, are decidedly superior in terms of the finder and mount.

How old do you estimate your vintage Bresser to be. I have always thought of Bresser as being pretty recent?

[John Huntley]

A decade or so back I had a Bresser 127L F/9.4 achromat. It was a really nice performer and I enjoyed it. I onnly let it go when I started to play around with 150mm F/8 achromats and a Chromacor CA / SA corrector. 

 

A couple of years later I came across a Meade AR5 which appeared to be the same scope as the Bresser 127L - it looked identical apart from the branding.

 

With the Meade though I could not get a really satisfying star test no matter how much I checked and adjusted the focuser and objective tilt, retaining ring tightness etc, etc. 

 

After some months of trying I concluded that the Meade AR5 was simply an example with a mediocre objective whereas the Bresser 127L had one of the better ones. These examples seemed to demonstrate the extremes that could come from that manufacturing source and the lottery that can present to the buyer.

[CHASLX200]

A decade or so back I had a Bresser 127L F/9.4 achromat. It was a really nice performer and I enjoyed it. I onnly let it go when I started to play around with 150mm F/8 achromats and a Chromacor CA / SA corrector. 

 

A couple of years later I came across a Meade AR5 which appeared to be the same scope as the Bresser 127L - it looked identical apart from the branding.

 

With the Meade though I could not get a really satisfying star test no matter how much I checked and adjusted the focuser and objective tilt, retaining ring tightness etc, etc. 

 

After some months of trying I concluded that the Meade AR5 was simply an example with a mediocre objective whereas the Bresser 127L had one of the better ones. These examples seemed to demonstrate the extremes that could come from that manufacturing source and the lottery that can present to the buyer.

My AR5 was not so hot as well.

[Refractor6]

  Back in the age of the dinosaurs you could test in advance and pick a scope that did well on the star test {daytime source or nighttime targets in many cases} at the local long gone astro shop where I half lived in the early 2000's.

 

That's how I purchased the Jinghua made achromats similar to the Meade or Bresser models mentioned that I still have today.  Yes I encountered poor samples during testing from a variety of Chinese sources that came into the shop.

 

 Sample variation certainly plays a factor in the difference between the really good ones and not so good ones.....

[Princess Leah]

Was Bresser always part of Explore Scientific company?

[maniack]

Was Bresser always part of Explore Scientific company?

Bresser is not part of ES and has been owned by JOC since 2009. I believe ES is currently an independent reseller of JOC products but was under partial JOC ownership for a few years.

[RLK1]

Chromatic Aberration is only ONE component of the image formed by a telescope's objective.

I, apparently, am not that sensitive to it and a little bit doesn't seem to get noticed by me.

On the other hand, there other a number of OTHER characteristics of a refractor's objective that really DO make a difference in the viewing experience.  

Lens figuring, lens polish, coatings, the overall match between the individual lens elements, the degree of correction (over/under etc.),.... all of THESE aspects GREATLY affect the sharpness, contrast, field curvature or flatness, and other discernable attributes of the image which, to me, are far more important to the viewing experience than a tiny bit of CA. 

 

I'll take a finely engineered, well configured, superbly polished, well matched, flat field Achromat with everything done right over a lesser quality FPL-53 (or whatever) objective lens ANY DAY!

 

I expect ALL aspects of an achromatic objective lens to generate the best possible image and CA is only but one consideration and it is certainly NOT the most important one on my list.   

 

PEACE, 

Bobby 

Kalamazoo, MI 

Well, I gotta say, that when I see claims that a 6" F5 achromatic refractor, for example in various posts from time to time in reference to a Jaeger F5 refractor, have what is described as quote "minimal"chromatic aberration, I have to laugh. I mean to hear them tell it, the CA hardly exists!  Either the poster, IMO, is color blind or delusional or simply fooling themselves because I've seen 6" f5 achromatic refractors in the field and the CA in them is horrible!  

 

I do have a 6" F 6.5 Antares achromatic refractor and it's much better on the CA than an F5 will ever be and while I agree the other optical properties noted in the above post are exceedingly important, the amount of CA in a fast achromatic refractor, seemingly popular among some observers,  is overt and omnipresent and discounting it to the degree that I've seen it stated as so in these forums is disingenuous in my opinion. 

[CHASLX200]

F/5 would kill me unless for a sweeper creeper at 30x pow wow.

[John Huntley]

Was Bresser always part of Explore Scientific company?

Originally Bresser was a family run company run from Germany. One of my first proper telescopes was branded Bresser but made by Vixen. The Bresser model designation was The Uranus while Vixen called it the SP102M. It was a very good F/9.8 102mm achromat fitted with an early GOTO system called the Skysensor. This photo was scanned from an old 35mm print, hence it's poor quality:

 

Edited by John Huntley, 20 April 2025 - 01:13 PM.

[RLK1]

F/5 would kill me unless for a sweeper creeper at 30x pow wow.

For all the reasons noted in post 516 and then some at 30x!...

[Gonariu]

How old do you estimate your vintage Bresser to be. I have always thought of Bresser as being pretty recent?

It's a Bresser from someone I know in my village and that I had the opportunity to try in September 2024.

[Princess Leah]

Originally Bresser was a family run company run from Germany. One of my first proper telescopes was branded Bresser but made by Vixen. The Bresser model designation was The Uranus while Vixen called it the SP102M. It was a very good F/9.8 102mm achromat fitted with an early GOTO system called the Skysensor. This photo was scanned from an old 35mm print, hence it's poor quality:

 

post-17685-0-33818800-1622243915.jpg

Lovely nostalgic photo John.

Thanks for explaining the history, very interesting.