26 replies to this topic

[phxbird]

 

On January 16 2025 Morrison Observatory at Central Methodist University had an open house. Before the observing time started I used my handheld cellphone to image Venus. Here is the results. Both images are the same but one is as it appeared on the screen and the other has been tweaked slightly in Light Room. 

 

This summer the 12.25" Alvin Clark Refractor will be 160 years old. There are a lot of comments about the quality of these telescopes. I read with amusement the statements in past discussions that these telescopes are of "poor quality", "inferior build" and other such comments. Ralph Nye the retired engineer from Lowell Observatory rebuilt the 24" Clark refractor and the 13" Pluto refractor at Lowell Observatory. In measuring and testing the optics as they were disassembled, he found that the lenses were as good as any that could be ground today. Poor quality and construction are not an issue!

 

In doing public nights as well as labs for my astronomy classes there is another major reason that some really dislike these types of historic refractors. Some of my students are like me and just don't see as much of the purple surrounding bright objects. Others have trouble focusing their attention on the planet or star because of the "purple haze." I suspect some of the detractors just can't look past the purple. 

 

For their time the Clark refractors were state-of-the-art instruments. Our Clark was used for the first modern scientific papers on Jupiter's Great Red Spot. They still give a wonderful view of the stars and planets often to people who have never looked through a telescope before. 

 

Paul Temple

Director of Morrison Observatory

Central Methodist University

 

 

 

[vidrazor]

In doing public nights as well as labs for my astronomy classes there is another major reason that some really dislike these types of historic refractors. Some of my students are like me and just don't see as much of the purple surrounding bright objects. Others have trouble focusing their attention on the planet or star because of the "purple haze." I suspect some of the detractors just can't look past the purple.

Well, what would you expect?

 

It would be interesting to see if modern-day corrective optics could be added to the scope, especially if it can be done at the eyepiece. This would leave the scope intact while correcting for it's ancient design and formulation.
 

[J A VOLK]

I view through the 1895 24" Clark at Lowell regularly.  The optical quality is stunning - Ralph Nye is right on - if optics could be figured better it would be in the noise.  I have looked through numerous Clark scopes, up to 150 years old - each and every one has been superb. 

[Airship]

Sometimes the purple can be distracting, but I have found that if I take a moment to relax and take in the view my eye suddenly "sees" the fine detail in the image and the purple fades into the background. It always amazes me what I can see when I look. 😀

[CHASLX200]

Should do 1200x easy.

[YourNotSirius]

I am so envious that you get to use that monster. My dad would be willing to do "nasty things" for that privilege. We can't say what they are due to the mods being so squeamish about such things. Someone might be "offended"! BWAHAHAHAHAHA!

 

Anyway, we have a stable full of refractors and some do have a slight haze when pointed at bright objects like Venus. Some don't. We are of the opinion that the brain can be taught to filter it out and thereby not become a cry baby over it. Some cannot accomplish that task. Too bad.

 

As for the "Purple Haze", the best answer is to turn on Jimmy Hendrix and listen carefully to it, at full volume! HOORAH!

 

Q

[mikey cee]

Too dam bad you can't find an avatar like mine 'floating' around anymore. Even a Baader semi-apo filter can help a great deal. Try one. What do you really have to lose. A nice old Aries Chromacor of any flavor I'd die for in your shoes. Mike      

Edited by mikey cee, 27 January 2025 - 11:50 PM.

[John Higbee]

Paul - couldn't agree with you more...the lunar and planetary views we routinely achieve using the United States Naval Academy's  Alvan Clark 7.75" refractor (obtained in 1858) provide exquisitely sharp and detailed pictures for Midshipmen and Academy personnel!

 

All the best, John

[CHASLX200]

Too dam bad you can't find an avatar like mine 'floating' around anymore. Even a Baader semi-apo filter can help a great deal Try one. What do you really have to lose. A nice old Aries Chromacor of any flavor I'd die for in your shoes. Mike       aries-chromacor-n-rare_161652876113.jpg

I found one in my flooded mess. Paid a arm and leg for it for a 8 i had plans to get and never did get it over 20 years ago.

[starman876]

I found one in my flooded mess. Paid a arm and leg for it for a 8 i had plans to get and never did get it over 20 years ago.

You have a chromacor?

[Jeff B]

Well, what would you expect?

 

It would be interesting to see if modern-day corrective optics could be added to the scope, especially if it can be done at the eyepiece. This would leave the scope intact while correcting for it's ancient design and formulation.
 

The short answer is yes, as Mikey has shown, and I have demonstrated with our 11" F12 D&G achromat.  Both of us use Chromacors to good effect.  But our use of the Chromacor is "off label".  It would be best to custom match a sub-aperture corrector to such big achromats.

 

So, the objective's actual performance must first be documented as best as it can be.  Even though the design and glass may be "ancient", most are still common, two glass achromats, using normal dispersion glasses and spherical surfaces.   To do a real, at least medium confidence, analysis, the objective would have to be measured in DPAC, star and interferometric testing in the red, green and blue, then taken apart and the elements physically measured. 

 

Software would help determine probable/best fit glass types that best match the physical and optical measurements.  Then the design of the sub-aperture corrector can begin.

 

And then there is that pesky fabrication thing......

 

But it most certainly can be done.

 

Jeff

[CHASLX200]

You have a chromacor?

Little wet and moldy. Just as well throw it out it's done now.

[starman876]

If you want to sell let me know

[Don W]

Ok guys, this is not classifieds

[phxbird]

I haven't used my old Celestron Minus-V filter onb our refractor yet. The color hasn't been all of that objectionable. However, in the next month or so we are hoping to use a QHY camera to image Mars and Jupiter through the Clark. Will the image be better than a larger SC or modern APO refractor...no probably not. But it would be historic!

[Airship]

Just for yucks you might also try a Baader Semi-Apo filter, it combines some additional filtering to help balance the color after removing the blue end resulting is a somewhat warm color palette. These filter ban work rather well on large refractors where you can tolerate the light loss in the filter. I have done a fair amount of imaging with long achromats and they can give excellent fields and sharp images in the red and green, though they tend to rollover in the blue. There are several techniques to manage the blue rollover, but that's another thread. Bottom line, long achros can make excellent imaging platforms.

 

Enjoy!

[mikeDnight]

 These lovely old achromatic refractors are simply fabulous. I did have chance to use a 7. 25" Clarke refractor at Stoneyhurst college back in the 80's. It was a jawdroppingly good lens.

 

 With Venus however, CA will nearly always be an issue if the planet is observed against a dark sky background. Far better to observe it in daylight I feel.

 

Not an old Clarke, but still top class, is my modern FC100DZ.  A Venus scope if ever there was one!

This sketch is from the late afternoon of January 27th 2025 without the use of any filters. North is top and a binoviewer and 128X magnification used. (Prism view).

 

[phxbird]

Nice Venus sketch!

[fjjoachim]

I have never viewed Venus through an Alvan Clark refractor telescope, but I did get to view Saturn through a 36" and Jupiter through a 12" Alvan Clark refractors on Mt Hamilton in California. I almost had a chance to look through the 40 inch Clark refractor in Williams Bay in Wisconsin, but I was thwarted by thunderstorms.

 

Nice drawing of Venus by Mike!

[jragsdale]

I have a fondness for the Morrison 12¼" Clark (1865) as it's a close relative to the Westleyan/Peltier Clark 12" Clark (1868). I'm hoping to have this scope finished this year so I can start viewing with it.

[deSitter]

Little wet and moldy. Just as well throw it out it's done now.

Send it here, I'll clean it up. I can't believe someone who gives up so easily enjoys fishing.

 

-drl

[deSitter]

If you can make something so large it looks like a pizza, no one will care about a colored fringe. Remember the Conrady criterion is an absolute. A purple rind on a tiny gibbous Venus will be a lot more bothersome than the same amount of rind on a huge disk that occupies the entire field of view. Likewise if you are looking at Jupiter so large and bright that the colors pop and sizzle as if it were next door, you're not going to care about a tiny rind of purple.

 

I imagine Saturn is so breathtaking through one of these large scopes that no one cares a fig about the color, or even notices it much.

 

-drl

[starman876]

If you can make something so large it looks like a pizza, no one will care about a colored fringe. Remember the Conrady criterion is an absolute. A purple rind on a tiny gibbous Venus will be a lot more bothersome than the same amount of rind on a huge disk that occupies the entire field of view. Likewise if you are looking at Jupiter so large and bright that the colors pop and sizzle as if it were next door, you're not going to care about a tiny rind of purple.

 

I imagine Saturn is so breathtaking through one of these large scopes that no one cares a fig about the color, or even notices it much.

 

-drl

the image scale at that aperture with that focal length must be breathtaking.  

[Steve Allison]

I remember reading a quote somewhere where the speaker stated that the view of Saturn through the Lick 36 inch was the greatest sight ever beheld by man.

[CHASLX200]

Send it here, I'll clean it up. I can't believe someone who gives up so easily enjoys fishing.

 

-drl

No one can fish offshore like i can stan.  I can get em in sleep. I sold it and guy is gonna pick it up.