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jefrs

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Posts posted by jefrs

  1. I've tried to use a "Dandelion" AF confirm chip/adaptor and it was about as much use as a chocolate teapot, fortunately it soon snapped itself in half.

    All it ever did was fool the camera into thinking a lens was fitted but they don't need that, It was supposed to put the green focussed lamp on but never did.

    M43 uses the "shoot without lens" setting for manual lenses.

    Our M43 camera mostly all have focus highlight "peaking" which works with any lenses even manual ones. Only the older ones do not have this function.

    Reflex lenses "doughnut" when out of focus and hence are reasonably easy to judge even without focus highlighting, but the long lens image dances about like mad when you touch the focus ring. And there's my problem, I can't make micro-movements with my fingers: I may drill and tap the alloy focus ring (there is more then enough metal thickness) to fit a focus-lock screw that would also serve as a long lever for micro adjustments, something like M3x80

    Good sky tonight but freezing, my left hand is practically non-operational this evening, second and  third finger feel like someone stepped on them: I'll have to give my experiment a miss today :-(

  2. "Its light Jef but not as we know it" ;)

    Coincidence but someone has dropped me an email offering one for sale (600mm f6.3) at about £90.

    How does it perform during the day. I'm trying to decide if the time for the drive will be worth it.

    Cheers,

    Rich

    They're not that much more new, I think I paid £130 for the 800 f/8 and £120 for the 500 f/6.3

    As with all reflex and indeed such long lenses you lose sharpness and contrast and they have a very shallow depth of field of something like 1/2-nch wide at 3 metres.

    This deficit is easily boosted up by the camera or in post.

    Image quality not the best but about the best you cant get at this length without selling body parts e.g. Nikkor 600mm f/4 £7,000

    I say at this length because I'm using them on M43 (MFT) which has a x2 crop factor so the 800mm is equivalent to a 1600mm on full frame (and it has a x2 teleconverter)

    I have used them for wildlife, some pics on my wall here https://www.flickr.com/photos/jefrs/ you'll have to sift but I always give description and exif: usually sooc jpeg unless I crop the rw2 raw: I refuse to photoshop every snap. The robin was taken at length of garden and filled the frame,  I adjusted sharpness and contrast at the camera. Not the best image quality by any means but it can be that of no image. I know Canon also do a reflex (500mm?) I've seen the results and not noticeably better.

    The focus movement is little more than 1/4-turn and the infinity end is closed up (logarithmic scale) plus my arthritic fingers were numb with cold: I was disappointed not to resolve  circles but another nudge and I got doughnuts.

    I shall try to focus astro again but on a stiffer mount where I'm not stretching; the moon may be a better target.

    • Like 1
  3. I know there are some strong opinions regarding the jumper starter power pack offerings and strong opinions on leisure batteries etc.

    Personally, coming into astronomy as a newbie it was a bit daunting, people advising not to go with power packs, other saying go self build etc. Well I eventually bought a 20Ah Ring Automotive power pack (RRP110) from Amazon. I have had no complaints with it yet (2 years). I charge it up after each session and every month or so and when using it it will happily allow me to slew around with the 8SE and run a dew heater for several hours (3-4) and it will use a third or less of the power (according to the in built meter).

    Now if I intended on going for a better mount, for all night sessions with multiple dew heaters, powering CCDs etc. I would definitely go with a self build leisure battery and I might eventually change it out, but for initial getting started, I'd recommend a power pack, they are plug and play and imo ideal for starting out and to get aquatinted with everything.

    You're good to go with a battery supply system. But caveat :-)

    Accumulator battery car jump starters have to exceed the voltage of a fully charged car battery i.e 14VDC - they are not 12 volts

    Which is fine if your 12V equipment has some form of voltage regulation. Which is very easy and cheap to arrange so I'd be surprised if the scope etc doesn't have this

    However the mains powered jump-start battery chargers are very coarsely rectified (no smoothing) and provide over 14V in order to charge the 14V battery in the car (12V is essentially the car battery's minimum operating voltage under load). These things can damage electronics applications, attaching one to the car battery smooths the current and regulates its voltage. They can also provide the enormous current needed by a starter motor; I have used industrial versions for arc-welding thermocouples. And we don't want a 12V >200A supply to a scope.

    I have checked a number of wall wart power supplies with the DVMM and found they rarely output what they say on the case, they usually rely on the intended equipment to have a regulator. If that  equipment is a motor then they don't bother with smoothing the output current (DC electric motors work best on un-smoothed current)

    At present the most efficient batteries are the AA type. I favour the stay-charged rechargeable variety although they are only 2Ah, I can get them recharged in 15 minutes and they remain fully charged for months, which the false-economy higher charge versions don't.

  4. I shot a time lapse series on the Sky-Watcher Star Adventurer EQ with the Panasonic GH4 to test the Samyang Reflex 500mm f/6.3 (8 seconds at ISO800)

    In the middle of the series, this one shot stood out.

    P1140045cropt

    It's been post developed in Elements and cropped but not massaged (Elements doesn't actually convert the raw as well as the camera does: £45 software vs £1300 camera? go figure)

    The lens is very difficult to focus, even with the manual focus assist x6 digital zoom on, and suffers badly from vibration (the optical image stabilised (OIS) Lumix G 100-300/F4.0-5.6 fares far better)

    Tripod was the medium weight Manfrotto 055XPROB

    The lens also seems to suffer from distortion/aberration but its sibling the Samyang Reflex 800mm f/8.0 fares worse. The stars appeared conical but could not be focussed circular; suggesting the focus mechanism needs finer movement at the infinity end of travel or it is just not man for the job.

    Interestingly perhaps, the Panasonic GH4 and Lumix G 100-300/F4.0-5.6 combination later scored a perfect auto-focus lock using the pinpoint focus mode (confirmed by MF) on Sirius.

    Sirius blew out the highlights impressively so I swung it over to the Pleiades where we acquired focus confirmation highlighting on the Pleiades cluster stars with manual focus (MF).

    This was an equipment test on the patio where we have too much light pollution for decent viewing. Aligning on Polaris through the sodium yellow haze is particularly tiresome.

    • Like 2
  5. Coated mirrors are washable in water using care and a few drops of dish soap, followed by a rinse with distilled water.  It is misleading to say other wise IMHO http://www.loptics.com/articles/mirrorcare/mirrorcare.html

    Coated mirrors ok but distilled water is even more corrosive than tap water and the latter will leave a residue.

    Distilled water has no salts in it to act as a buffer and so it can act as acid and alkali at the same time OH- & H3O+ and it is very, very corrosive, it will eat stainless steel, which is why it is only carried in plastic containers

    De-ionised water is different again, it is what we put in batteries and steam irons..

    Soaps and detergents are ionising surfactants and can and will find any scratches in your coating through to the shiny aluminium and it's goodnight Vienna.

    I've made mirrors and coated them in the lab. Aluminium has to be coated immediately or it magically turns into sapphire (ok alumina then) I'd stick to the iso-proply alcohol.

  6. I also like the forum, and am not so much a fan of the lack of editing.  As a former mod on another forum though, I can see why it is done.  Although, if a post is edited before a mod sees it, then surely the self-editing is a good thing?  At least it means that posters are realising their mistakes and redacting it themselves.   Although I realise the mods cannot then give out warnings for offending posts, based on the word of another member.  However, if another member is so offended by a statement, they could quote the post for evidence, the OP cannot then edit another persons post.

    My reason for liking to edit is that I often hit the "Post" button prematurely, and often miss out pertinent information, which I can usually go edit the post and add the info.  On the other hand, adding in an extra post has allowed me to reach the required 50 post count to view the classifieds a little earlier, so it's not all bad news.

    jfrs, I feel your pain.  My spelling can often be terrible too.  I use google chrome as my browser though, with it's built-in spell checker, and if I make a mistake, it is highlighted (underlined in red), and easily rectified with a right-click on the mouse button and selecting what I had meant to write.  I'm sure most web browsers have this feature, whether it is disabled or not I wouldn't know.

    50 posts might be a bit high to be able to see the classifieds IMO.  25 seems more reasonable to me.  I'm guessing it is to prevent spam posts in the classifieds, but it just encourages it elsewhere in the forum, as evidenced above me.  And to have this rule, coupled with the lounge posts not counting towards post count, means the spam is in relatively more important parts of the forum.

    Beyond that, the website seems fine.  And the information, both already on, or offered in help, appears to be first rate.

    My spelling is pretty good. My professional work often involved writing reports as technical author but you get a proof-reader with that. I'm also married to an english teacher. Problem is my fingerts are dyslexic now, I can barely type: osteoarthritis in every single joint and spondylitis in the bits that aren't joints. Strangely, a good work out on the guitar improves things. I use Firefox and have a spelling checker running but I probably have twice the vocabulary of its lexicon. Bless Noah Webster for he was truly dyslexic.

    I too will hit post and then realise I've made a pig's breakfast of it: I can easily type numbers in reverse, or say "can" when I meant "cannot" (rather significant).

    Ho-hum, until we get accepted as grown-ups I guess I'll just have to make another post and another post to correct stuff as corrigenda.

  7. Thanks jefrs - that's great advice. I'm going to try and find the right adaptor and give it a try. I like the value of the EPL5 right now so will probably buy that one.

    For adaptor rings I would Google up one of our telescope specialist companies and then phone them to make sure you get the right thing. Imo it's not the usual Ebay T2 to M43 adaptor ring we want.

    The "T" is for Tamron, not Telescope and it's a M42x0.75 metric thread (as opposed to the Praktica M42x1.0 lens mount), but "M43" is "micro four thirds" naming a lens mount system that uses a "four thirds" (4/3)  size sensor.

    I now have several adaptors. The normal length when mounting a legacy lens e.g. Pentax-K is about 35mm from sensor with a M43-PK adaptor. T2/M43 adaptors can come as 35mm length from sensor for reflex lenses or without the 2cm extension tube, some have a tube that usefully unscrews. There is about 15mm from mount to sensor and OEM M43 lenses are designed to focus the image at that range.

  8. Thanks jefrs - that's great advice. I'm going to try and find the right adaptor and give it a try. I like the value of the EPL5 right now so will probably buy that one.

    It's a nice pocket camera but you might also look at the Panasonic G6 which will give you the much needed remote shutter release: should also be cheapish - under £400 w.lens, less than £270 used i.e. similar prices to E-PL5 but the E-PL7 is only a little more (and big upgrade over the E-PL5). My G5 cannot do time lapse but apparently the G6 can. Having said that the G5 has a remote socket so I can use the time lapse feed from the motorised EQ mount.

    The E-PL7 is an updated E-M10 without the EVF but having both flavours I can baldly state that the Pannies are better built: I had a switch knob fall off an E-M1 and the shoddy plastic hot shoe cover for the E-PL7 self destructed. Unlike entry-level DSLR the kit lenses on M43 are pretty good glass, although the 14-42EZ does have reports of jamming and which is why I use the PZ14-42 on the E-PL7.

    My E-PL7 does suffer from a hot sensor when shooting video, burst shots and long exposures, wrong camera for job. My Pannies (except wife's GX7) have the sensor firmly mounted on a heat sink, they do not get hot. Keeping the sensor cool can be important for astro work.

  9. I re-read the OP's post.

    Rob is considering the E-PL5 which is probably discontinued hence should be even cheaper than the E-PL7 which has many better features than the E-PL5/6. The E-PL6 was a cosmetic upgrade but the E-PL7 is a big step, I think they are trying out some stuff for the new E-M5 mk.2

    One advantage of Panasonic over Olympus for this work is the sensor is mounted on a heat sink, hence less noise from long exposures which do heat the sensor up: the sensor is right behind the monitor screen and the back does get warm to the touch, which produces "hot pixels". The G5 has an allow body frame and the GH4 chassis is designed as an effective heat sink; they stay cold. I have never used the G6 but it has more features than the G5 and could be ideal.

  10. Sorry, they do not understand "compact system camera" :- The Olympus Pen Lite E-PL7 has interchangeable lenses. The E-PL7 is not a "compact" camera. It is an updated E-M10 without the EVF.

    The E-PL7 is a mirrorless micro four thirds system camera: I have one and it is compact, it is my "pocket" camera, it's fun to have a tiny 16Mp camera that takes top quality pics.

    The sensor on M43 cameras is some 2cm closer to the mount than a typical DSLR e.g. Canon, because it has no mirror.

    Yes it can mount with adaptor on the telescope focus mechanism with the correct adaptor(s)

    The E-PL7 has no remote cable shutter release but I suppose we can use WiFi control.

    The E-PL7 tilt screen is at all the wrong angles on a telescope, so is wife's GX7. The 130SLT is actually my wife's telescope, as I'm a physicist-engineer (radiological metrologist) I get to be the tech support.

    Hence I prefer one of my Panasonic M43 with their fully articulated screens. My G5 cannot do time lapse, my GH4 costs an arm and a leg.

    Mirrorless cameras do have the sensor exposed when the lens is removed (permanent live view). I got some black smuts on the sensor changing the lens in the dark (I can clean sensors but prefer not to) Be careful. Hence I recommend always fitting a Barlow and/or eyepiece in a clean room to seal the sensor housing up: black smut problem solved.

    Due to the short sensor to mount distance I am getting some issues with back focus. I find something like a thin adaptor ring onto a 2X Barlow w/o eyepiece or a 2cm M43/T2 adaptor onto a "short nose" is giving best results so far as other configurations with an eyepiece inserted seem to want the camera closer to the secondary mirror than the focus mechanism will permit. Either that or I get very severe vignetting. If an eyepiece will fit inside the T-adaptor i.e. 37mm long, then an eyepiece can just about be used; most are longer or too wide.

    I have not solved this yet, in fact I came on the forum just now to see if I could find out how others are mounting cameras to reflectors.

    My alternative is to put the camera on the Star Adventurer EQ mount with a 500mm or 800mm reflex lens i.e. a telescope lens, but that lacks the Goto of the Celestron. I am old enough to remember clockwork EQ mounts Alignment can be fun because you have to see Polaris and it doesn't always cooperate.

  11. I keep all my gear in a garden shed. However the Newt have reptile heating pads on the back of the mirrors.

    These provide a gentle heat at 6W. I also try and open up the shed to circulate air and keep the temperature down when it heats up. You can get them quite cheaply on ebay from China, about a third of the price of pet shop ones.

    Initially without the pads I found insidious dew/ humidity on the mirrors when temperatures changed. If I'm sure of observing that evening, I remove the pad and open a door up,

    Nick.

    Interesting (!)

    Of course the other big shed problem is mould, we can get mould on lenses as well as my leather bike saddles, and a new big shed (with mains power) in the spring is planned for me (I'll have to clear extra ground and shift a pair of 1 tonne compost bins, I've already booked a mate to help). My old shed has disintegrated.

  12. We use the colour change type as it tells the user that they need to regenerate.

    We have a free Rh & Dew Point calculator on our website http://michell.com/uk/support/sware-downloads.htm quite useful to work out the dew point of the day/night. Use the Relative Humidity button.

    We used the colour indicator desiccant in many of the instruments the department calibrated, useful but it's not the only method. You can buy bagged or loose silica gel right cheaply from industrial suppliers. Big bags, bigger is better, too big is just right. When I retired I was running an international primary calibration standard. Our reference Rh, T&P meters were calibrated by primary lab. I intend to get several half-kilo bags for the scope and camera aluminium storage cases (not the carry bags) and rotate them in and out; about the size of a bag of sugar. A cloth (lens) bag full of dry rice will also work but not nearly as efficient, so will common salt but you can get corrosion everywhere.

    I put two 1 kilo bags intended for a car in the car. The maker reckoned one bag was enough, two is not enough, I estimate at least six are needed in wet weather. These are regenerated on their weight; when they go over 1500g put on radiator. It is heat input that regenerates them not temperature (chemistry): you can use a low-low (plate warming) fan oven; we used lab convector ovens at work.

  13. Whilst setting up in the house I found the view bleary and so unscrewed the eyepiece, they had used enough grease to service the wheel bearing on a car and got it all over the graticule disc. So I had to dismantle and wash it clean in iso-propyl alcohol (lens cleaner): there should be just the merest smear of grease on these screws not great blobs. If you ever grease these things then use half as much as you think you need and then divide that by two.

    So then I had fun with the 1.5mm Allen key, good job I've got tools because they didn't provide (I'm part engineer). Having used bow-spring compass dividers on the collar to get the graticule in and out it needed basic realignment; it was way out. I've got maybe 30 paces from scope to kitchen. The view is reversed L to R to it was counter-intuitive: tightening a screw pull the graticule towards it but you can only loosen and nip up the other two, and it's back to front; you need point of reference, which way am I moving, a dot in the sky is not good. The torque settings on (any) screws this small is minute; less than my finger-tight. The book advises no more that 1/4 turn on any adjust and I concur. My nominal 30 metres (4 cars parked) seems to be a sufficient distance to do this. I do need to check down the garden and beyond, I've got a telegraph pole about 100 metres away that makes a good aiming sight.

    I couldn't  get at Polaris due to heavy rain and solid cloud cover :-(

  14. Amazon has a Vello sony alpha to t-adapter for like 10$ US

    Probably 100$ shipping plus customs tax then. It's weird, it's actually much cheaper to import from Japan than the USA. No idea why.

    Japan can get stuff over here air-freight in under a week but HK/China 12-16 weeks if you're lucky.

    If using Amazon or Ebay in the UK then best to check where it's sellers are based and shipping from. UK and France are good. Germany are fast and efficient, often have stuff we don't but for some reason they bump the price of optics up 50-75% over UK price. For Japan for hard to find stuff, you really need to be able to read japanese, fortunately I've got a friend who can ... :-)

    However with a telescope the OP may need a different back focus to a normal lens adaptor, even a selection of tubes (different length T2.M/F) to add in to adjust focal length on a short adaptor: i.e. find one of the telescope specialists on-line and give them a phone call, talk to them.

  15. Polar finder is a good app but I am not sure if its PC/android only.

    Alan

    Thanks, I put "Polar Finder" into the iTunes app search engine and returned two "PolarAlign" (2.1 and 5.1), one entirely in japanese and one for finding icecream ;-)

    PolarAlign 5.1 can't seem to  access the iPhone GPS but PolarAlignAP 2.1 locks on immediately.

  16. Visited another member off here yesterday, he runs an electric blanket on low and a dehumidifier in his Obsy to keep condensation at bay. Keeping scope outside otherwise must have an effect

    I have an electric oil-rilled radfiator in the workshop, it keeps dampness off my tools, I know first-hand that these work in a shed

    Set at zero it will maintain a room frost-free but that is too cold for me.

  17. If you have the type of silica that changes colour it can be baked in an oven at 150C for an hour or so to regenerate it.

    I use this type in a piece of Rh calibration equipment and it works quite well.

    Metal tubes (OTA's) mirrors and lenses do not cool down just to ambient, if they did it would not be a problem. They cool by radiaiting heat off and this cools them to below ambient which depending on the conditions will hit the dew point and then of course water condenses out as you change from gaseous water vapour phase to liquid phase behaviour.

    The difference between ambient T and dew point T does not have to be large, in fact as little as a single degree can be enough.

    It does not have to change colour, you can weigh it. I keep a coulple of 1kg bags in the car, when they get to 1500g they need regenerating on a radiator.

    Heat and tremperature are misunderstood subjects. You need to consider thermal conductivity: metals readily conduct heat which makes them feel cool when at ambient. Ye cannae break the laws of thermodynamics ;-)

  18. May I please ask what software or app you use for polar alignment of celestial north (or south) on an eq mount such as Sky Watcher's Star Adventurer?

    I've only found one for the iPad/iPhone "AstroPhysics PolarAlignAP 2.1" (phew).

    Is this any good?

    Are there others to consider?

    Any iPhone app is handy because the GPS knows we are, plus the handy-size thing is in my pocket instead of hauling a 15-in laptop out :-(

    TIA, Jeff.

  19. You can estimate accuracy with the tangent angle i.e tan = perpendicular / base. (down & dirty)

    it we assume the target spot has an apparent 1mm diameter and the distance is A = 10 metres or B = 100 metres

    (the target spot cancels so it does not matter what size it is; it is the same both times, we could call it "n")

    then

    tan(x) = 1/10,000

    and

    tan(y) = 1/100,000

    therefore the angle ratio is

    x/y = 10

    (we don't really have to go through that lot; it's "show working")

    i.e. it is 10 times better to increase the distance by 10 : the accuracy (field of view (FoV) angle) is directly proportional to the distance.

    The garage wall test may confirm if your finder is good enough or way off the mark and you need to take it outdoors to calibrate: I can see line of sight clean through our house which is guesstimate six or seven car lengths; probably not enough to calibrate the finder but good enough to check whether it needs resetting.

    I would not recommend making any adjustments indoors, you'll only need to re-do them  (I spent many years operating a calibration laboratory).

    I'm setting up / playing with a Star Adventurer tonight. Although we're 51°N it's not that cold outside but it is completely overcast: no Polaris yet :-(

    • Like 1
  20. Last night here in Newbury it was quite remarkable how the sky could clear completely of cloud in under a minute, and cloud over again just as fast. It was not drifting in, it would dissipate and then re-form. Weird really, I've seen patches do that but not noticed the whole lot go before.

  21. I usually take a minimum of 3000 frames. More if my tracking's OK. It makes a big difference!

    I worked in calibration lab for, a long time, ran a primary standard. When we did multiple readings of erm, stuff, we would limit that to 6 because the statistics show us that an increase above that spreads the data out and we lose vital information. Above this the s.d. (sigma) tends to get bigger rather than improve. The stats is post-grad stuff to do with how to sample data and I don't propose to go into it here really ;-)

    The optimum point for multiple sampling (applies to stacking photos too) is around n=5, v=5.

    And yeah, I let the camera run in time lapse for 1800 to 2400 shots too and pick the best ones. But if the samples are too far apart in time I find they don't align (stack) well.

  22. Doughnuts or donuts are characterisic of an out of focus reflector lens. The DoF in front of the (any) lens is shorter than the DoF behind it. One can use the visual appearance of doughnuts to aid focussing by finding the mid-point between their formation. The stars are effectively at infinity but focussing can go past infinity (diverge), this applies to extra-long camera lenses too.

    Of possible interest the DoF of a 800/F8 reflex lens at 3 metres is approx 1/2-in :- not very much. Consequntly telescopes can be a pain to keep focussed.

    Whilst I can and do use the camera's focus confirmation on the moon (it will even AF on with the right lens), the moon is not at infinity, near enough but not quite good enough for deep sky.

    The camera won't confirm focus on stars although I did get lucky with the Orion Nebula when it did a pinpoint AF on it for me with an extra-long staibilised (OIS) lens: that indicated to me that the lens was not on its end-stop.

    tpyos are feature :-)

    • Like 1
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