Tuesday, July 17, 2018

20180716 Mars

I woke up again in the mid-night to take these, again it's 20180717 in terms of local time (GMT+8), but then the title above is in UT.

Manual focusing was used, I've installed the Rigel Quick Finder on the 85ED and alignment was a breeze.

2004 (UT), 85mm ED f/6 with 5x Powermate

2011 (UT), 85mm ED f/6 with 5x Powermate stacked with 2x

Similar level of detail, but Mars is so bright that is tempting for bigger image scale.

Monday, July 16, 2018

20180716 Jupiter, experimental stacking of 5x and 2x

It is a very windy day, a typhoon will be passing by soon.  Expect very poor seeing but then it's rather decent at 6-7/10, nearly the best I can ever experience at home!  Transparency like 6/10, it's a very good night for me.

As usual, I used a 5x Powermate to capture two shots, drizzle is not used:

1304 (UT):-

1307 (UT):-

I didn't use my motorized focuser yet, because it's still being fine tuned.  Manual focusing is do-able with some more patience... the second shot was taken in attempt to improve the focus, but it seems similar.

Encouraged by the visual testing this afternoon, I pushed the 85ED again by inserting a 2x barlows after the 5x, which means f/60 at least, I estimate it to be f/66.7

1313 (UT):-

No more detail can be obtained over f/30 with the 5x Powermate alone.  Just an equipment test.

Magnification limit of the 85ED

This is a small aperture, short focus refractor... but with the help of the FCD1, let's see how much we might push it.

The test is conducted during day time with distant objects.

First up is a 20mm eyepiece, so we have 510/25 = 25.5x, image is exceptionally sharp.

And then I inserted a 5x Powermate, and it yields 128x, image remains very sharp.

Replacing it with a 4x TMB, i.e. same magnification as about, this eyepiece is sharper.

My floaters come in... I got a couple of annoying floating within this year, I'm getting old.

Insert a 2x barlows, we have 255x and image is still very sharp, but of course, it's getting dim with only 0.33mm exit pupil.

I don't expect to be able to see anything, I used a combination of 5x with the 4mm TMB... which means 638x!!!  Crazy me... I racked the focuser in and out, finally got a sharp but very dim image at 0.13mm exit pupil!

No image break-down!

With the Ranger, such a magnification was spoiled completely by the chromatic aberration.

Thursday, July 12, 2018

20180711 Mars

It's 20180712 already in terms of local time, but the title is in UT.

Other than the world cup, woke up for the first shot of Mars for this apparition... really dusty!

2102 (UT)

Manual focusing was used as the electric focuser is under revamp, it's still doable with some patience.
85mm ED with 5x Powermate, 1.5x Drizzle as usual.

Wednesday, July 11, 2018

20180711 Jupiter as a test of the DIY electric focuser

Made a quick and dirty first version:

Still need to find better way to mount the motor so that it could be fixed along the OTA direction.

Anyway, it works.

We got 0.1/10 transparency, the Jupiter was a fuzzy patch of light with naked eyes.  I've to push the gain to maximum, and shutter to something like 0.3-0.5 second to get a very dim image. 

Manual focusing is impossible under this situation and it also proves that the electric focuser indeed worked.

1409 (UT), and I got only 200 frames due to the long exposure required for each exposure, and thus a very low frame rate.  Anyway, it is just to test the focuser.

Tuesday, July 10, 2018

My new 85ED refractor

It has been a long time since I bought a brand new telescope.

My brand new telescopes include my first scope Celestron C90, and then a Tele Vue Ranger.  Later a C8 and then everything else was second hand, including a Takahashi Sky90, a couple of C5, ETX 60, PST, a 5 inch Maksutov, etc.

This time I got a 85mm ED refractor.  The Tele Vue Ranger is really out dated in terms of its lens, don't get me wrong, it's a perfect achromatic refractor but that's all.  For H-alpha solar observation, it still performs exceptionally well because it's well figured.  For monochromatic light, it's unbeatable even compare with modern day FPL-51 or even FPL-53 based refractors!

Okay, let's go straight to this little new guy:

The core is its objective, it's a 85mm lens at f/6 with focal length of 510mm.  Very close to my Ranger which is 480mm.  This guy is actually a bit faster.  At f/6, even a FPL-53 based refractor would be hard to be a real apochromatic, not to say this is just a FCD1 based (similar to FPL-51) one.  This scope was advertised to have FCD1 matched with H-TF3L, but whether H-TF3L is special enough apart from a simple flint, I don't know.

The scope looks very nice.  It comes with a rack and pinion focuser, with dual speed knobs.  Focusing is smooth.  It's a 2.5" focuser and it comes with 2" and 1.25" adapter with compression ring.   The focuser is rotatable.

The tube rings are very nicely machined.  The including dovetail is a bit too short, I've replaced it with my Intes and it's just about right length for better balancing.

And worst yet, the original dovetail is too short to fit in my Nexstar mount.  Even a long camera tripod balance plate works better, as shown below.  Notice that if the dovetail is shorter than the clamp saddle, it simply won't fit in:

I've checked the tube and there is no light baffle inside, just like the Ranger with dull black sand finish, not bad and it keep its weight low.

The paint job is not very good, there are some missing paints here and there.

The dew shield is retractable, so that at its minimum, and it's about the length of my Ranger.  Very portable indeed, and I've enough room inside my dry box.  Of course, this guy is heavier, nearly 1.5X of the Ranger.

And the tube rings:-

with the Intes dovetail, the original one should be lighter.

I've removed the left focusing knob and replaced it with a brass gear, and I handheld a small DC geared motor there and they mesh well.  I shall make mounting hardware for it asap.  I deadly want motorized focusing as always.

Enough modification for the first day, em?

Guess what, I'm lucky enough to take a test shot with Jupiter during the first night!  It's less than 3 hours after its arrival.  Seeing was very poor but then at least I can tell, the chromatic aberration is far better than my Ranger, at half the cost twenty years ago!  When inflation is taken into account, I get a very nice deal indeed!  I hope this is going to be my work horse for planet and general observations.

I will keep my Ranger solely for solar works, and I believe the Ranger might still be better than this new refractor in terms of monochromatic solar imaging.

Due to the fact that I already had my Canon FD 300mm f2.8, it makes not much sense for my to buy the field flattener for this scope.  The next step might be a 2" diagonal plus a 2" wide field eyepiece, but then I shall be using my Canon 18x50 instead?  Let's wait and see, there's no need to rush.

Maybe motorizing the focuser and attaching a Rigel Quick Finder are among the first priority.

20180710 Jupiter and a new telescope

I sold all my telescopes except my Tele Vue Ranger.  But then I wanted to look at the planets and I soon realized that the chromatic aberration is annoying.  I don't need aperture, and I need to keep portability so a better refractor is a normal step forward.

I didn't buy a new telescope for a long time.  I did buy some 2nd hand telescopes, and an absolute new one might be my C8?  This time, I bought a FCD-100 based ED refractor.  Let's see an image taken tonight first:

1342 (UT), taken with a 5x Powermate, we have the GRS on the lower left.  I'm pretty confident that this little new refractor is going to perform quite well.

Seeing was extremely poor, and cloud was floating around.  I got a single AVI after waiting for a long time.

A separate article will be written on the first night impression of this refractor, at less than half the cost of the Ranger twenty years ago!

Saturday, July 07, 2018

20180706 Jupiter (missed the shadow transit)

I didn't do this kind of shots for many years, maybe like 10 years!

Too bad that cloud rolled in, and I missed the shadow transit!

A small telescope could bring much fun, I shall keep on!

Thursday, July 05, 2018

Conclusion about the Canon FD 300mm f2.8

The conversion is very easy, and could be done with off the shelf parts, and such conversion could be easily reversible.

When a 2x barlows is inserted before the diagonal, it could be used visually with an eyepiece.  It is not bad as a wide field telescope.

However, high power performance suffers especially with bright objects.  It is because it is a telephoto lens, so the flare and internal reflection renders it useless.

I've tried every effort to remove the internal reflection but in vain.  The problem must be in the unmodified part of the optical chain.  On looking at the inside through the objective, I believe that the internal unblackened parts could be the source, but I've no way to verify.  The protective element before the flourite lens could be another source as well... but again, I've no way to verify.

So this lens will be reserved solely for imaging purpose.  It is still a very nice 300mm f2.8 astrograph, it's very compact, light weight and thus highly portable.  It's also very well corrected.