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Frequent Contributor
Posts: 60
Registered: ‎11-16-2015

Re: Bower 500mm fixed lens NO AF.

[ Edited ]

The folks who write "The Photographer's Ephemeris" also have an app named "The Photographer's Transit".

 

Fantastic shot!

 

Just took a look at the blurbs about both of the above products online. Seems that they are free, which seems like a fair price to me. They are also available for PC, which is good for me because I am the only person in a developed country who still doesn't have an iPhone.

 

Most of this subject is over my head, but I'll get tutored somehow later. I'm still studying the basics of our solar system; that is, how the earth, moon and sun work together throughout the year.

 

Norm

 

PS. Through more online research, I finally figured out how the app that I posted earlier works. However, it would seem that the above s/w's are more germane.

 

 

 

Frequent Contributor
Posts: 60
Registered: ‎11-16-2015

Re: Bower 500mm fixed lens NO AF.

[ Edited ]

Addendum: Since you are an astrophotography aficionado, I suppose that you also use a telescope w/camera from time to time. If so, must you buy a separate tripod and head, or will those used for zoom lens w/camera do?

 

Norm

 

Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: Bower 500mm fixed lens NO AF.


@Norm53 wrote:

 

Just took a look at the blurbs about both of the above products online. Seems that they are free, which seems like a fair price to me. They are also available for PC, which is good for me because I am the only person in a developed country who still doesn't have an iPhone.

 

 


I know you can get "The Photographer's Ephemeris" on a PC and that is free (last I checked it's a Java application ... which means it'll run on any computer -- Windows, Mac, even Linux.  

 

But when I checked the price of the smart-phone app... that was not free.  (e.g. Photographer's Ephemeris was $8.99 -- or you could get the "Photographer's Ephemeris" and "Photographer's Transit" bundle for something like $12 (that's from memory -- so I might be off on that price.)

 

 

Tim Campbell
5D III, 5D IV, 60Da
Frequent Contributor
Posts: 60
Registered: ‎11-16-2015

Re: Bower 500mm fixed lens NO AF.

Might have been a free trial offer. Anyway, the prices won't break the bank.

 

Norm

 

Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: Bower 500mm fixed lens NO AF.


@Norm53 wrote:

Addendum: Since you are an astrophotography aficionado, I suppose that you also use a telescope w/camera from time to time. If so, must you buy a separate tripod and head, or will those used for zoom lens w/camera do?

 

Norm

 


 

So there are two different answers to this question.

 

I do attach the camera to a telescope and MOST of the time that's what I'm doing.  But all of the telescopes I use are either on something called (generically) an "equatorial" mount (meaning that the axis of rotation is aligned so that it is parallel to Earth's axis of rotation -- roughly the north star although that star is technically about 2/3rds of a degree away from the true pole.)  If the mount is not precisely aligned then the stars will all seem to "drift" in the field of view very slowly.   Visually you will think things are not drifting... but when you use a camera to take an exposure merely a couple of minutes long you'll notice everythign is smeared from the drift caused by an imprecise alignment.   

 

Normally even if a mount is precisely aligned, there is enough mechanical error that your tracking wont be smooth enough to have no blur in the image.  Variations in how perfect the worm gear is made... or imperfect orthagonality of the mechanical axes of the scope, etc. will cause some grief even when you align "perfectly".  To get around this problem, astronomers use soemthing called an "auto-guider".  It's a 2nd camera mounted on the telescope and all it does it take a photo of the same area of the sky... but every few seconds (whereas the main imaging camera might be recording an image for many many minutes... 5 minutes, 10 minutes... it could be as much as an hour.)  But the auto-guider isn't trying to find faint detail in a deep-space object... it just wants to track the position of a reasonably bright star that would easily expose within a second.    It compares the position of that star in the frame from the original position to detect if the star has drifted (even by a tiny amount).   If it has drifted, then it sends a corrective movement to the telescope mount to put the telescope back on track.  It does this continuously and at the end of a very long image the object you want to photograph will not have moved by even so much as 1/2 of a pixel.

 

So the first answer is that I'm using telescope mounts.  My "favorite" mount is my Losmdandy G11 which has, so far, given me staggeringly good results.  So far I've managed 8 minutes "un-guided" imaging with nearly no perceptable drift (it's rare to be able to go much longer than 4 or 5 minutes but my mount.)  I know about a half dozen other astro-imagers that use the same mount and their mounts (while good) aren't able to get away with unguided images as long as me (so I appear to have won the proverbial lottery and happened to get a copy of that mount which has better-than-typical performance.)

 

But there is a second answer... which is that I did recently acquire a special "head" which attaches to a photographic tripod and allows me to use a regular camera and lens and not need a telescope.  This means I'm getting wider field images (instead of imaging one particular deep space object I'm imaging a larger area of the sky... perhpas big enough to hold an entire constellation ... perhaps big enough to occupy quite a huge area of sky (Milky Way images, etc.)  I've only recently acquired it and haven't put it to work (yet ... but it's coming with me on a trip in January and I expect it'll get heavy use.)

 

That system (the Losmandy StarLapse) does go onto a normal camera tripod but you want a "beefy" tripod (nothing too springy or flexible -- you're trying to eliminate vibrations).  Also, while it could be mounted to my normal head (I use a Benro BH3 ballhead), it's much easier to attain precise polar alignment with a video head.  I have a Benro S8 head and a Benro S4 video head (the S8 head is much stronger but I think the S4 head may do the job.)

 

If the load is not too heavy (smaller lenses) then you can get away with lighter solutions -- such as a Vixen Polarie or iOptrion Sky Tracker.  I prefer the Losmandy (not an assembly line product... these are built in a machine shop one at a time... which drives up the price, but the precision of the product is so much better.

 

I've mentioned this elsewhere... you don't necessarily need a head that "tracks" the stars to do astrophotography.  If you want landscape in the foreground then a stationary head is better BUT you want a very wide angle lens.   For a camera with an APS-C size sensor, divide 375 (that's your baseline) by the focal length of your lens (e.g. if you have a 10-22mm ultra-wide angle zoom for example but you're using the 10mm focal length) then you'd divide 375 ÷ 10 = 37.5 and that result is the number of seconds that you can leave the camera shutter open and NOT get elongated stars due to the rotation of the Earth.

 

Tim Campbell
5D III, 5D IV, 60Da
Frequent Contributor
Posts: 60
Registered: ‎11-16-2015

Re: Bower 500mm fixed lens NO AF.

But there is a second answer... which is that I did recently acquire a special "head" which attaches to a photographic tripod and allows me to use a regular camera and lens and not need a telescope.  

 

Getting back to the moon, does a telescope w/camera on a photo tripod (with appropriate head) produce moon images that a zoom lens w/camera on that tripod (with appropriate head) cannot produce?

 

Norm

 

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Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: Bower 500mm fixed lens NO AF.

[ Edited ]

@Norm53 wrote:

But there is a second answer... which is that I did recently acquire a special "head" which attaches to a photographic tripod and allows me to use a regular camera and lens and not need a telescope.  

 

Getting back to the moon, does a telescope w/camera on a photo tripod (with appropriate head) produce moon images that a zoom lens w/camera on that tripod (with appropriate head) cannot produce?

 

Norm

 


Yes - it's more to the "angle of view"

 

The moon has an "angular dimesion" of about 1/2º from edge to edge.  

 

If you take a photo of the moon with a 300mm lens on a camera with an APS-C sensor ... you can use this page to find the angular field of view:   http://www.tawbaware.com/maxlyons/calc.htm

 

If you scroll down to where it says "Angular Field of View Calculator" you can plug in the values "300" for focal length, "1.6" for crop factor (the default) and leave the aspect ratio at 3:2 (the default for any DSLR) the click "compute" you'll see the angles.

 

The horizontal angular field of view is 4.3º

The vertical angular field of view is 2.9º

 

Knowing that the moon is only 1/2 degree you can quickly see how you can fit nearly 6 moons in the "short" dimension of your field of view and and just over 8 mooons in the "long" dimension.  This means you are going to have a rather tiny moon.

 

If you want a large moon that fills the frame, you'll need something around 1200mm (the moon shots you've seen me posts were taken through a telescope at 1080mm and I cropped just a tiny amount.)   This really helps when you want to see detail.

 

The loony 11 rule still works... so if it's an f/11 scope then it's ISO 100 and 1/100th sec exposure.    It'd probably shoot it at a much faster ISO and faster shutter speed if on a mount that isn't tracking the skies.  Otherwise a "tracking" mount is preferred. Since the exposure time is short, it doesn't put great demands on the quality of the mount.  When you shoot long exposures (e.g. 30 seconds or longer) that's when investing in a better mount really pays off.

 

The longer the exposure and the smaller the area of the sky that you image, then the mount needs to be better (short exosures are more forgiving and wider field images are more forgiving.  I recommend starting with those.  Very long and very narrow field of view images are the hardest (and have the greatest demands on a very good tracking system to keep the telescope on target during the entire length of the exposure.)

 

 

Tim Campbell
5D III, 5D IV, 60Da
Frequent Contributor
Posts: 59
Registered: ‎10-20-2015

Re: Bower 500mm fixed lens NO AF.

It's funny, but i just grabbed it one night and the full moon was coming up and took some really cool pictures! It was very detailed and like you said underexposed. I was even holding it by hand and was amazed that they came out pretty clear.

Frequent Contributor
Posts: 60
Registered: ‎11-16-2015

Re: Bower 500mm fixed lens NO AF.

Thank you, Tim, for your inspiring presentations.

 

Norm

 

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Posts: 11,491
Registered: ‎12-07-2012

Re: Bower 500mm fixed lens NO AF.

"It was very detailed and like you said underexposed."

 

Underexposure is much better to deal with in post than overexposure.  Especially if you shoot RAW and not jpg.

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