Thursday, April 30, 2015

A large piece of glass!


70mm refractor on the left and 300mm f2.8 lens on the right... as an amateur astronomer, we all love aperture!

My very first autoguiding exercise

The Sky Adventurer has only single axis guiding, so it would require good polar alignment to guide successfully... of course, it's rather hard to do indoor.

Finding a bright enough star is not easy too... but I managed to get one.  The polar alignment was rather off despite the target star stayed in the field for quite long, and that indicates not too bad polar alignment.  However, it did drift away slowly and PHD guiding was complaining.

Cloud moved in before I could try EQ Align to fine tune the polar alignment.

Now at least I know that my ASI 130mc and the ST4 port of my Sky Adventurer works, I will need a better night to try the whole thing again.

A small DEC motor was on order, together with some electronics, and I will try to make my Sky Adventurer with dual axis motor/guiding.  Not very confident, but why not have a try?

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For dual axis guiding, the guide scope and the imaging scope  should be on the same side of the L adapter, so the balancing side should carry something heavy as well... is that making the whole thing meaningless in that case?  The Sky Adventurer is wide field and portable!

I guess I will be taking a 200mm lens for my trip, so the polar scope should be enough and no need of guiding.  So, I will be bring a 50mm lens, a 200mm lens plus a 2x tele extender and that's all.  The 300mm f2.8 will be left at home.

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To test the concept of using camera lenses as guide scope, I found that I have to insert a 2x barlows in order to reach focus with a camera lens.  It's good in the sense that, the guiding lens is always working at higher power!  Suppose I have two lenses, 200mm and 300mm respectively.  If I use the 200mm as imaging scope and the 300mm as guide scope, the guide scope will be working at 600mm due to the barlows.  Even if I swap their role, the 300mm as imaging scope and the 200mm as the guider, but then the guiding side will still have 400mm focal length!


Wednesday, April 29, 2015

Sky Adventurer dual axis guiding

The Sky Adventurer features a ST4 style guiding port which allows RA guiding, but that also means it only correct PEC.  The DEC part is manual driven only, so we couldn't guide in a dual axis way.

Motorizing the DEC part is the first step, here we have two approaches:


The one on the left is to use an inline shaft coupler, I got one at home which matches quite nicely.  Problem is that, the motor would make the whole thing much more bulky.  The next method is the one on the right, it uses two gears, one on the original manual control knob and another one on the motor, but I got only one such gear ready at home.  I will need to buy one more and the motor could be placed below the DEC body, I will want a smaller motor in that case, and I will also need to find a way to mount the body and mesh the gear correctly.

The following wiring scheme could be used:

Guider -> 
ST4 port of my own, getting the DEC signal to drive the motor -> 
ST4 port of the Sky Adventurer

So no need to modify the Sky Adventurer, just add a "relay box" and steal the unused DEC signal.  A simple geared motor controller could be used to drive the DEC.  Too good to be true?  Best of both worlds?  Let's see... I shall start hunting for suitable parts.  We need gear with 6mm shaft bore.

Further downsizing: Skywatcher Sky Adventurer


This is a huge move again.

My GOTO Mark-X is very portable but yet, it requires a "heavy" 410 geared head, and it is rather heavy and bulky as well.  So here I go for an even smaller mount.  This mount should be able to do astrophotography and it should be able to let me use my C5 visually or for planet imaging.

First of all, the tripod that I'm going to use is a Velbon mini-white.  It is ultra-portable as you can see from the above picture on the right.  It can even sneak within a lens compartment of my Fastpack 350!  Next is the Sky Adventurer, the mount body could be hidden in a lens compartment of my Fastpack, too!  The polar wedge is lighter and easier to use than the 410 geared head, and again, could be fitted into a lens compartment.

This is what I have fitted within the lower padded compartment of my Fastpack 350 as shown above:

Upper left: Canon 50mm f1.8, plus a ASI 120mc for guiding.

Lower left: Skywatcher main body which is a self contained mount with hand controller and battery compartment, polarscope!  It even features an ST4 style guider port!

Upper middle: a Velbon mini white tripod, frankly, it's even more miraculous than the Sky Adventurer and they are also a perfect fit.

Upper right: polar wedge for the Skywatcher

Lower right: a Canon 200mm f2.8L

Also a Canon 70D with a 8mm fisheye lens

What's left is a L adapter containing also the DEC body on the upper compartment, and the notebook computer in its own compartment.  Too good to be true, right?  A simple backpack containing all the lenses, tracking mount with guiding, guider and camera!

The picture on the right is the testing setup.  It takes a Ranger without any problem and I would say a C5 is easy for this small guy with proper balancing on the other side of the L adapter.

Monday, April 27, 2015

20150427 Sun

Heard that there's a long filament these days, and I got time at home, so why not?

First up is a prime focus shot stitched from two shots at 1431 and 1432 respectively.


Then we have 3x shots:

1434 (GMT+8), this one is aimed at taking the filament and prominence in a single shot, but it's too big to fit into the field of my Lumenera Lu070M.


AR2327 and AR2311, taken at 1437 (GMT+8):-


An exposure aimed at the prominence, and it shows more detail than the 1434 shot.


An exposure aimed at the filament, and it shows more detail the 1434 shot as well.


Enjoyable short session.

Friday, April 24, 2015

Dedicated Guidescope?

I am thinking about the need of a guidescope which is important for astrophotography.

However, if you're going to bring several camera lens for different focal length, we might actually use them to guide each others.  For example, if you're going to bring a 200mm f2.8 and a 300mm f2.8, they might be able to serve as the guidescope of the counterpart with suitable adapters.

In case the focal lengths are quite different, say 100mm and a 300mm, a tele-extender might be added to make them close.  We know that the guiding accuracy might suffer if you use shorter focal length to guide longer, but that's what you have to live with when we want absolute simplicity.

Remember the good old days, my friend used a FS60C and Sky90 in that way with great success.

Conclusion is that, for relatively wide field imaging, and I know that 300mm is pushing the limit, we might not need a dedicated Guidescope.

Tuesday, April 21, 2015

Selling my GOTO Mark-X

It's a very great mount, high capacity, compact, precise, and the most important thing is that, it's a working piece of history, a collector's item.

But still, I'm moving to lighter weight stuff.  So here we go, if you're lucky enough to see this, feel free to make an offer to me.  I have a reserve price in mind, but why not just offer and ask?

Here is a few pictures of the mount.  First of all, the controller and the motor is not original, but from Carton which is the OEM of the discontinued Tele Vue System Mount.  The speed of the motor could be fine tuned by turning a small knob inside the hand paddle.  It supports both northern and southern operation, and it has stop and 2x mode.


On the back of the paddle, there is a detachable battery pack of two 18650 Lithium batteries.   A set of two will last for many observation sessions.  The battery pack could be attached to the back of the hand paddle neatly as shown.


So, it could be removed any time.


The black motor mounted on the Mark-X.


A U-adapter was mounted securely on the Mark-X, with one side with a worm geared driven DEC slow motion control block and GP style dovetail saddle, the other side was a 3/8" screw which allows attachment of a ball head, I will throw in a good ball head if the offer is good enough.


Another view of the mount, the mount body is very new indeed.


Finally, everything could be packed in a small padded camera bag which is included in this deal.


Thank you for looking, and waiting for any reasonable offer.  If there is no offer within a week or so, I will put it on local astronomy forums.

Sunday, April 19, 2015

The Quest of a 4" refractor/astrograph: experiment and fine tuning (Canon FD 300mm f2.8)

As an amateur astronomer, I have several Canon EF adapters lying around. I found this one to be perfect for such purpose, since there are three fixing screws so that you can turn the M42 thread again the EF mount!


So the orientation of the lens could be fixed easily!   Note the pencil mark I made above in order to find out the best orientation.


QED.

Tonight, I have conducted photographic and visual test.

Visually, it's sharp at low magnifications.  I have used a diagonal by placing a 2x barlows lens in front of it, serving as a relay lens.  It could reach focus without problem.  Pushing the power will result in softening, unacceptable I would say, and it looks like internal reflection due to the extra lens elements on the rear part.  My primary impression is that, this is not a good visual telescope, and it is not going to replace my C5 therefore.

Photographically, it's great.  It's very sharp and free of any color fringes.  On pushing it with a Kenko 2x, I found that it will produce error, but of course, if I use a M42-EOS adapter with built-in chip, the error will go away, and I will have focus confirm signal too.  So, I will need to buy myself a rotatable M42-EOS adapter with built-in chip, and then the project will probably close.

Conclusion: this is a very nice camera lens, but not exactly a great telescope.  I found that my 200mm f2.8L suffers from the same problem, while the Canon 100-400mm is a great telescope, however.  Faster lens is not really good candidate for visual purpose at high power.

Saturday, April 18, 2015

The Quest of a 4" refractor/astrograph: implementaton (Canon FD 300mm f2.8)

After removing that three little screws, it's still pretty hard to remove the rear part... but then I've a tool which was used when I was disassembling my PST before!  With it, it could be done rather easily!

Rear assembly removed cleanly:


The 77mm P0.75 male thread was left:


I'm getting excited!  With the M77-M58, M58-M42, M42-EOS adapters in place, we have the following compact 4" refractor with 300mm focal length!



The amount of 77mm thread is enough, on the contrary of my previous imagination!  Next, the flange distance is correctly made for EOS with a single extension tube.  This becomes a very fast f/2.8 compact refractor!  Unluckily, when all the adapters were screwed together, the orientation of the built-in tripod socket was in a bad position, I have to find a solution for that.

 
The above configuation allows infinity focus without any problem!  The built-in focuser is butter smooth despite it is a very aged lens.  Canon L series is really really serious!

To switch it into visual configuration, the extension tube should be removed, and a EOS-1.25" adapter is used.  Unluckily, the amount of optical path length is insufficient for a star diagonal.  The following picture shows how I could reach infinity focus with an eyepiece.


This is a 300mm wide field refractor, with my 20mm widescan, it yields 15x with 5.3+ degree field of view, very sharp and respectable!

To use a star diagonal, I must insert a 2x barlows in front of the diagonal, so it becomes a 900mm focal length telescope.  The exact focal length must be measured.  I must try to use it for planet imaging soon, and if it's good enough, I shall sell my C5.

Keywords: Canon FD 300mm f2.8 conversion EOS digital EF mount astrograph telescope flange distance eyepiece M42