Someone said, everyone should have a 4" APO. This is somewhat a magic number of aperture that thing remains portable and affordable, and it provides very nice visual and photographic potential.
To me, I want to remain light weight and absolute portable, and of course, I want to keep the cost down as well.
Several candidates from my mind:
1. Takahashi FC-100DC, f/7.4 at 2.8kg only
2. Borg 100ED, similar to the above
3. Canon EF 300mm f2.8L (USM), very light and fast too, but double the price of the above
4. Canon FD 300mm f2.8L, cheaper than all the above but have to modify myself
5. Chinese ED refractor, like Skyrover, even cheaper than the above one but far heavier
So, the best balance points are Canon EF 300mm f2.8L without USM (the problem is that Canon is not going to fix them in case of any problem) and the Canon FD 300mm f2.8L which got no problem about maintenance since it has nothing to repair basically.
After removing the rear mounting assembly which also contains the aperture control, the thread is M77 P0.75 so it's relatively easy to find suitable adapters. And the best length from the M77 thread to the EF adapter seems to be 51mm according to the above site.
To get such an adapter with proper length, we have "大口径 中号调焦筒" from taobao, adapter are available from M62 to M42 featuring adjustable length from 28-62mm, very flexible indeed.
By connecting a M77 to M62 step down ring, the modification is done. Other cheaper adjustable length adapter could be used, they're of smaller aperture.
I hope that it could be used as a small telescope and telephoto lens. Time to search for those online reviews. Tempting.
On the next morning, I searched around my cabinet. The following adapters are useful:
First is a M42 to Canon mount adapter, should be useful if I want to couple the converted lens into a Canon EF lens, of course, manual focus only, no aperture control since it's removed.
Second is a M60 to 1.25" barrel adapter, useful to use the converted lens as a telescope. 1.25" is wide enough for a 300mm lens, 2" is probably over kill. But who don't want wider field?
So after the adjustable tube, I will need stepping ring with M60 male thread to connect an eyepiece adapter, and I will want M42 male thread to conect with a EF lens (mechanically only!)
Reverse macro rings could be used for EF lens coupling too.
And since 1.25" is smaller than 42mm, so it's safe to use a M42 adjustable tube with male thread as the output interface from the lens.
On choosing the adjustable tube, we need to consider the stepping rings.
M77 male from the lens --- adjustable tube -- M42 for EF lens OR M60 for eyepiece
M60 is not very common, so I will need one more ring...
Oh no.... simplifying the whole thing, I have an EF to 1.25" adapter! So, once the lens is adapted as EF lens use, I could use an eyepiece without any other concern:
So the solution boils down to...
M77 male from the lens --- adjustable tube -- M42 for EF lens
So I will need stepping rings from M77 to M42, to connect to a both side M42 adjustable tube and then to the EF lens adapter!
The optical path length of a 1.25" diagonal is like 7-9cm, so even the shortest adapter (i.e. a M77 reverse macro adapter, male-male need to resolve too) won't work. ... need to try!
1. Buy a suitable FD 300mm 2.8, wait for a good deal
2. Buy a M42-M42 adjustable tube, and then output EF mount, to use eyepiece, use existing adapter
Phase Two: buy a reverse 77mm tube to couple with existing eyepiece adapter, to see if I can attached 1.25" eyepiece without barlows....
No no no ....
I found that I could simply do the following:
1. Buy a 77mm female to female adapter (possible two step rings, one step up and one step down again, 82mm seems a good bridge)
2. Buy a 77mm reverse macro ring
So the connection will be like this
M77 male thread from lens ->
M77 female thread from step up ring say to M82 ->
M82 step down ring output M77 female thread -->
Reverse macro ring
So the above coupling will be shortest, and then I could use my existing pure mechanical macro extension tube (combinations) to give around 51mm and then the FD lens will be able to reach focus with EF camera.
To use eyepiece, the extension tube could be removed to give more in-travel to accommodate a diagonal.
Very simple now, just a reverse macro ring plus two stepping rings!
I guess I don't need two M77 ring.... maybe stepping down a bit before going to a reverse adapter a good.
Final solution after looking at those stepping rings:-
1. EOS - M42 (female) adapter
2. 42mm male - 58mm female adapter
3. 58mm male - 77mm female adapter
Should be shortest, cheapest and thinnest with off the shelf components.
I believe that I will need to use a couple of macro extension tubes to create proper flange distance. I really hope that it can reach focus without a barlows, then it will be a great rich field telescope too! In that case, even better than a 300mm f2.8L IS USM!
I got no time to shoot that extraordinary long filament... but it's not yet gone completely, so I caught the chance today.
The sky was full of scattering cloud.
Let's begin with 5x shots first:-
This monster prominence taken at 2400mm is bigger than Jupiter in size! I've never seen such a big monster in the last ten years!
And then we have AR2282 in close up:-
Let's go to 2x:-
This is that long filament, it's not unexpected that part of it was now out of sight. Notice that the filament extends rather far out to form a straight and tall prominence there, so we know how "thick" that filament actually is. This is a two frames mosaic.
That bigger than Jupiter prominence at 2x:-
Finally, we go for prime focus shots:-
My younger daughter Almy was on sick leave today, so she had a view on all those features... she loves the view too!
The sky was not particularly good, but it's not easy to go out either. I didn't take any planetary images for quite long and that's why I proceeded to a nearby playground to take some shots of the Jupiter.
Transparency was like 7/10, seeing 3/10. I was going out with the Nexstar SE mount and C5 OTA in a big plastic bag on one hand, and the tripod plus accessories in a backpack.
First one was taken at prime focus. The ASI refused to show anything, but on re-plugging and re-launching the software, it works finally. It seems quite sensitive but I don't like the larger chip and high resolution especially with my Eee PC, I have to scroll around to see the whole chip or I've to shrink the image at 50% but it was no good for focusing.
The Eee PC is now having a new Chinese 9 cells battery and it really has much juice to run on... after an hour of imaging, it's still going very strong.
Not bad and no good either. At least, I have much better images taken with my Ranger! Note the three Jovian satellites around.
A close up with 2x barlows, showing no more detail than the above.
One can see the direction of the wind blowing here... a signature of poor seeing.
Thank God that I can get another Canon 100-400mm f4.5-5.6L finally.
I sold my first one before the release of the second generation, but then my sister bought my a new 70D so I deadly want to get a longer lens to fully utilize its focusing ability, so with some very nice offering, I got one finally.
Given it has the same 77mm thread with my Ranger, so why not try it out on Solar imaging too? To use the BF10, I have a EOS 1.25" adapter, but to reach focus, I have to insert a 2x barlows before the BF10. Conventional wisdom gives an estimate with 3x, so the first shot was done at around 300mm effective focal length with the Canon set at 100mm.
The image quality is far from satisfactory. At first I would guess it's nice to take lower power full disc shot of the sun, but it's no good indeed.
Without much hope but just to complete the test, I set the Canon at 400mm, that means it's working at around 1200mm focal length. To my big surprise, it's as sharp as my Ranger! Maybe even better, I don't know. But it really shines! Very fine detail could be resolved with great contrast.
Okay, the test is done, so I switched back to my Ranger. To get a full disc, I've to take two frames and stitch them together. Transparency is no good today.
Then a close up AR2260 with a 5x Powermate, giving effectively 2400mm focal length. The first one was obtained by K3CCD, my usual software of choice.
But then since now I've ASI and thus I have SharpCap installed, so why not trying it too with my Lumenera? K3CCD was a bit troublesome, even I upgrade from Windows 8 to 8.1, it requires me to re-do the registration. And the author Peter seems not responding after one whole week. So, I switched for SharpCap.
With the software assisted focusing, the image seems sharper.
Drop frame is further reduced after removing some more software from my Eee PC.
The sky seems alright until now, maybe I shall try out 2014BL86 tonight after dinner?