Teething pains entering this great hobby

[Jessun]

Hello again!

I am still just learning the basics of observing/photographing, so far only in the living room trying not to stumble over all the cables!

I have scanned the web for knowledge and landed on a setup that just about blew my budget (by factor 2) see my signature.

Now I have a few initial questions:

First question is about the wheight issue when dealing with a mount: I still see the published payload figure confused with total load which includes counter wheights. I have concluded that payload means useful wheight excluding counter wheights. Right or wrong guys and gals?

Second question: There is a saying that for astrophotography that you should stick to no more than 50% of the rated payload. Where does this come from (apart from the fact that if enough people refer to it it becomes true)? This question is linked to the next one...

Third question: Assuming you have balanced up your OTA(s) with accessories, is this whole wheight issue not really a poorly covered up torque issue? I put it to you that torque is everything and that it's vital to keep all the mass as centered as possibly to reduce stress on the motors (for a misaligned GOTO mount such as mine ), meaning that a badly distributed 10kgs can cause more problems than a tight 15kgs? (Look at the tight roper's long pole!)

Fourth question: What is the point of 1.25"? Is it not beneficial to keep the aperture up all the way to the imaging device (eye or camera)? Ok cost (which I dearly appreciate..) , sure but strictly optically?

Fifth question: (software): I use TheSkyX and wonder if I should expect this to work alongside an autoguiding software such as PHD (which I find a genious piece of software... have yet to donate tho..)

Sixth question: (philosophical): What is the view amongst yourselves on all the modern gadgets to autoguide/find etc? I feel almost carried on a silver plate into this hobby with all the computerized gizmos at hand. So I bought myself a illuminated reticule to manually master dead on polar alignment, but what do you think? Do you approach a guy with a non computerized, painstakingly aligned scope shooting on film reels with utter awe or a sneer??

Seventh question: (optical) Ok, so I got myself a 0.5 focal reducer to be able to cover more sky and I read that this particular reducer needs about 100mm back focus. Do I understand this correctly that I need basically a 100mm tube between this reducer and my camera? Spiffing... since this reducer has 48mm thread and I have not yet come across extension tubes with this thread... (£45 lost...)

And finally a tip: Do not use oil paint to cover up the blue LED on the MS LifeCam Cinema . The paint is conductive and you will lose the whole green channel for ever when you plug the camera in haha! (£65 lost)

A well the teething pains...

Picture below is a screen capture of PHD guiding after about 30 min tracking... erm... a star... (I'll learn the names as I go along!)

All the best and perfect alignment to you all!

/Jessun

[hemihaggis]

jings , that lot will be a steep learning curve ! best of luck

[pete_l]

Phew! That's a lot of ground to cover.

1) Regarding weights. Yes, almost always the figure quoted is for payload. However, this adds up quickly - and don't forget the weight of the cables that dangle off your kit.

2) So far as downrating the 'scope payload limit for photography. It's not a hard rule and is largely arbitrary. What tends to happen is that as the payload (and counterweight) load increases, the inaccuracies of the drive system get magnified. Not by any consistent amount, and you could find that the "better" parts of your drive/worm-gears are capable of handling a load that the "squared-off" parts can't. As the load increases, the number of duff images you get will go up - all other things remaining equal.

3) There are two elements to consider here. The increased weight of the payload and counterbalance is all borne on the bearings and they do have a small, but finite amount of friction/sticktion. The greater the load, the less smooth their operation.

However, there is a property of moving systems called the "moment of inertia". This is to do with the energy in a moving system and the amount needed to start or stop it moving. Even if your system was perfectly balanced, so that just breathing on it would start it moving (before you tightened off the clutches), you still have to have enough torque in the motors to overcome the MoI and vary the speed of rotation to correct the guidance. As the weight increase and the distance out from the centre of rotation increases, you need to supply more energy to start/stop movement (ballerinas spinning faster as they move their arms inwards, thereby reducing their MoI but retaining the rotational energy - which gets translated into faster spinning). That's what you need the torque to overcome. It's also why you'd prefer to keep all the heavy stuff as far in to the centre as possible. While you could counterbalalnce a 10kg rig with a 5kg weight that's twice as far out, that would increase your MoI which is not a good thing.

6) On the point about philosophy, it's no different from a vintage car enthusiast talking to a F1 fan. Each to his/her own and we all respect the different skills needed and enjoyment that everyone else gets from their particular part of the hobby.

[Jessun]

Thanks Pete_l !

Good points there, never thought about bearing loads and friction!

And I appreciate your analogy about cars! I was curious since within many other fields of interest there seems to be a battle between old school puritans and the newer tech laden chaps. It is an encouraging view you take.

/Jessun

[Luke]

Hi Jessun,

Hello again!

Fourth question: What is the point of 1.25"?

I believe (but am happy to be corrected) that depending on your camera you may get vignetting using 1.25".

Sixth question: (philosophical): What is the view amongst yourselves on all the modern gadgets to autoguide/find etc?

For me use whatever you feel comfy with, goto, non-goto, autoguiding, manual guiding, it's all part of the same amazing hobby. I don't feel there's much sneering on SGL

Seventh question: (optical) Ok, so I got myself a 0.5 focal reducer to be able to cover more sky and I read that this particular reducer needs about 100mm back focus. Do I understand this correctly that I need basically a 100mm tube between this reducer and my camera?

Focal reducers normally need you to move the focuser inwards (inward travel), so an extension tube wouldn't help.

Barlows are the opposite and usually need you to move the focuser outwards, so in that case, if you haven't got enough outward travel, it's usually easily fixed by adding an extension tube.

Best of luck with the imaging!

Luke

[Luke]

Focal reducers normally need you to move the focuser inwards (inward travel), so an extension tube wouldn't help.

Oops, sorry, I've just realised the backfocus probably refers to the distance between the reducer lens and the camera chip/film!

I confused it with backwards travel of the focuser. Sorry!

[ollypenrice]

The percentage of payload that is useful for imaging depends of the manufacturer's honesty. Our Tak EM200 is rated for 15Kg. You can image at that, I think. The EQ6, which is a an inferior copy, is rated at 20Kg. The EQ6 is not better and you cannot image with 20Kg on either of ours. Some manufacturers like AP specify a difference between imaging and visual.

Balance and torque; balance needs to be nearly perfect but not perfect because you want the gears to fall to the same side of mesh, not oscillate across their own free play.

The length of the OTA and the extent to which it has high mass at a distance from its centre is hugely important in determining real payload, as you say. A Schmidt Newt has mirror and corrector plate at each end of a longish tube and is demanding. A short Newt only has real mass at one end... but if it is broad it will be demanding in the wind, etc etc.

What you need to avoid in DS imaging is vibration. Also the autoguider needs to be abe to recentre the OTA fast. Then there's focal length. Guiding at short focal length is 'easy'. Guiding at long focal length is very, very tricky! When you say 'I feel almost carried on a silver plate into this hobby with all the computerized gizmos at hand,' I suspect that you have yet to try getting 30 minute Ha subs without tracking error or field rotation throughout a long winter night... You may feel that there are challenges enough once you get going!

1.25 has no advantage other than cost but, if the 1.25 aperture does not restrict the light cone required by you chip it has no disadvantages either.

As for how somebody goes about astrophotography, my only thoughts are, 'Are they enjoying it?' and 'How good are their results?' Of those only the first one really matters in the end.

Olly

[Jessun]

Thanks for your input!

I can happily admit that I have not done a single second of Ha sub, and I am delighted to hear that it is utterly challenging! I am sure you know what I am probing for though. I personally have to dig deep in the roots of any hobby/sport i pick up to get that deeper sence of appreciation of what generations of pioneers have accomplished before I am air dropped into the zone with a stack of (hard earned) cash.

ollypenrice, I looked at your site and being new to this hobby and my girlfriend being a keen amateur portrait painter, I can see that our paths might cross one day!

I am still tripping over cables here trying to make sense of everything but enjoing every moment of it. I will learn a lot here!

/Jessun

[Sparrow]

An interesting read. Yes I often see the 50% figure mentioned on this forum when it comes to payloads. Personally, my rig is well beyond this and still performs perfectly well so I don't hold too much store by it (can't remember the exact figures for my set up now but did work it out some time ago).

As to your sixth question - well thank goodness for the modern gadgets - after all, it's digital photography and computers that have made the hobby far more feasable anyway. I remember when I was at school many many years ago, one of my teachers was an astronomer and had managed to get a blurry image of Andromeda which we all thought was super. It was a haphazard affair with an old DSLR and film. Imaging in those days was very hit and miss.

ENjoy the hobby and remember that it can be very frustrating at times - not every session will be a success and quite often it's a case of moving from one problem to the next - but when it all comes together, the satisfaction of a resulting image is wonderful. I still get a thrill when the first sub comes in and my target is in the frame to see.

Regards

John