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symmetal

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About symmetal

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    North Cornwall
  1. symmetal

    Sensor / reducer spacing question

    Glad you got some from FLO ok Tom. Hope the fitting goes well for you and that they make a difference. Alan
  2. symmetal

    Sensor / reducer spacing question

    Hi Tom, I don't think the 8 position filter wheel masks overlap as the 3 mounting holes are spaced evenly around the edge compared to the 5 filter wheel layout. I know this as FLO sent me the 8 position masks by mistake first time. I suppose ZWO issue the masks with the filter wheel as they are wheel specific. If sent with the filters they would have to include both sets, though this wouldn't be more costly really, as they would then not have to issue them to people who bought mounted filters. I thought the masks were only needed with the original filters which I assume aren't sold anymore, so was surprised that they issue the masks automatically with new wheels. I'm sure FLO would send you the masks if you bought the filters from them. I sent the 8 position masks back to FLO as I thought it would be rude not to as they're free, otherwise I could have sent them on to you. The masks are of a plastic material with one side smooth while the other side is textured. On the 5 position masks the only way to mount them is textured side facing the telescope if you're wondering which way to mount yours. While fitting them I lifted the filters out to check if they were the right way around but to be honest couldn't see any difference in the reflectivity between the two sides on the LRGB. Holding a screwdriver in front to check the reflections as recommended in other posts made no difference, so I put them back as they were. The other thing is the masks reduce the aperture a bit more. The 31mm diameter is reduced to about 29 by the original filter wheel mounting flange. Adding the masks the aperture is reduced to 27.5mm. I measured an 1.25" mounted filter and the aperture there is about 26.5mm. What a lot of hassle for 1mm. My ZWO Ha flats were a very weird shape and were also causing star halos so I swapped it for a Baader 31mm unmounted one. The Baader Ha flats were normal shape even without the masks. Alan
  3. Like you when I was taking short exposures with the ASI1600 the single frames did look very noisy and flat compared with longer exposures on my CCD and wasn't hopeful that stacking many more frames would make up for it but it does seem to work. The detail which seems 'lost' in the noise does re-appear when stacking 50 or more frames. So sticking to ISO 800 and taking 3 times as many 1 minute subs in the same period as your 3 minute subs, I think you will be surprised at the result. Just ensure your histogram isn't clipped on the left (on any colour) with the shorter subs, so that the skyglow signal is significantly more than the read noise. Alan
  4. symmetal

    Sensor / reducer spacing question

    Yes, I bought the 31mm ZWO filters with the 1600 in Sept 2017 thinking it would be a benefit if I got a larger sensor in the future. However, after all the hassle with the edge problems I wish I'd just bought the 1.25" mounted ones instead. I saw the threads like you posted and enquired from ZWO about supplying some masks. They replied that they would send some to FLO with their next shipment to distribute. I got them a couple of weeks ago. There are different masks for the 8 position wheel and the 5 position mini wheel which are really fiddly to fit trying to avoid touching the filter surfaces or the screwdriver slipping. Here they are on my 5 position wheel. As the 5 position filter wheel shares a common mounting screw between filters the masks have to overlap so don't sit flush with the surface. If you bought the first version ZWO filters from FLO they should have a set of masks to send to you if you ask, and they still have some left. Yes I believe that light is reflecting off the filter edges or the 'corner' where the flat surface meets the edge. Newer version filters have the edge blackening carried over the 'corner' while the originals didn't. Some colours of the original RGB filters didn't have any edge blackening. I imagine 'painting' the edges with a suitable matt black should have the same effect but would be even more fiddly. On the lights the problem usually seems to be most visible when very bright stars are in the frame, (or just out of frame) giving coloured 'flares' or halos. As the flats light source is not as bright (or pinpoint) as a bright star it doesn't give the same effect. Checking my flats pre and post masks again more closely, I have to admit there is little difference between them. I thought the SGP histogram was a better shape when I took the post mask flats but that doesn't seem to be the case. I haven't processed some images I took after the masks yet so can't confirm the difference with actual bright stars. Alan
  5. symmetal

    Sensor / reducer spacing question

    You're right . I assume your filters are the new version which don't have the edge artifacts that my original 31mm filters have. I only fitted the masking rings from ZWO last week to hopefully cure the problem. The flats from the masked ones are certainly more of a normal 'flats' shape compared to the original ones which had multiple 'humps' so hopefully will be an improvement. I normally have to resort to the Baader variable spacers to get the spacing optimum. Alan
  6. symmetal

    Sensor / reducer spacing question

    From the flat end body of the reducer which the spacer will butt up against when screwed on. Your distance calculation is about right. From the focal length spacing chart I would put it nearer to 63 to 63.5mm. Filters are usually 3mm thick so you would then add 1mm to the overall spacing distance (1/3 thickness). This comes to 64.0 to 64.5mm total. Subtracting your 26.5mm filter wheel and camera distances this comes to 37.5 to 38.0mm much as you said. You could try the 40mm spacer and see what the corner star shapes are like but I think it will be too long. I found that 0.5mm makes a noticeable difference in star shapes on my ZS-61(360mm) and ASI1600. Alan
  7. As the background skyglow (the histogram peaks) is the faintest object detail you can resolve, once this skyglow peak is not clipped to the left of the histogram there is little to gain by exposing for longer. The signal to noise will be improved to a degree, but your dynamic range will decrease and more stars will be clipped and bloated. In CMOS astro cameras it's normal to expose long enough for the camera read noise to be swamped by the skyglow and then take many exposures at that exposure duration. This is dependent on the gain and offset of the camera. For me, with the ASI1600, the swamping skyglow level is around 1400 ADU (in 16 bit) This would correspond to only around 2% on the histogram (linear display) For luminance exposures at unity gain this can be as short as 15 seconds in light polluted skies. I have fairly dark skies so can expose up to about 60 seconds before the skyglow limit is reached. With your one-shot colour DSLR these exposures would be about three times longer. I would aim initially for the centre of the histogram peak to be around the 15-20%% mark on the APT histogram (in linear mode), but not clipped on the left. On your darkest 02:45 image it's shown at around 30%. This would mean shorter exposures than your current 3 minutes at ISO800 or dropping the ISO. ISO800 is generally considered optimum for noise on Canon DSLRs so I would leave it at 800 and drop the exposures to 2 minutes or 90 seconds and so enable you to take more exposures to stack in the same imaging session. This will give you less star clipping, a larger dynamic range, and the increase in number of exposures should improve your noise when stacked. As your background skyglow, shown by the histogram peaks is fairly neutral in colour I don't believe a light pollution filter (if that's the sort of filter you had in mind) will achieve much. As your DSLR is modded you could try narrowband Ha which will allow you much longer exposures before you're limited by the skyglow. Other people may have other views and disagree with me, but that's my pennyworth. Alan
  8. The histogram peaks correspond to the level of the sky background. At 02:45 the sky will be darkest so the histogram shows the lowest level of background. At 7:08 pm there will still be some skyglow from the Sun even though it may be classed as Astro Dark. Astro Dark isn't a fixed level of darkness but is a threshold value below which it's considered dark enough for Astro. For a couple of hours after the Astro Dark threshold start time the sky will get darker. Alan
  9. symmetal

    baader on ebay

    They are on the Baader site (better picture) for 27.5 Euros and on Amazon (same bad picture as on ebay for £30.14 Alan
  10. symmetal

    Hardware rather than software

    USB2 and USB3 use separate connections and circuitry in the USB3 connectors and hubs and they don't interact. Well they do use the same 2 USB2 power pins for +5V and 0V. The 5 extra pins in the USB3 connector (compared to USB2) are for USB3 data only, while the original 2 USB2 position pins in the USB3 connectors are for USB2 only. Data+/- are USB2 only. Receive +/- and Transmit +/- are USB3 only. The extra Ground connection between the USB3 pins is a reference ground and is not meant to carry any power current. If any component in the chain is USB2 only the USB2 pins will be used for communication throughout. So a USB2 device plugged into a USB3 hub will have no effect on USB3 devices plugged into the hub apart from possibly taking a little bandwidth of the total available, but as USB2 uses only 1/10 the bandwidth of a USB3 connection the performance hit on the USB3 is not significant. Two USB3 devices plugged into a hub will have a more significant effect on each others performance as the available bandwidth has to be shared equally between them. Alan
  11. symmetal

    Power supply for SynScan EQ5 GOTO

    Yes, that power supply would be OK. It is 2.1 x 5.5mm, centre positive which is what you need. 5A is sufficient too. Alan
  12. symmetal

    Recommend me a filter set

    The Baader beginners set are absorptive filters (coloured glass) and won't have the pass band accuracy to match the more expensive dichroic filters. They will have more overlap between colours and less transmission. I assume the similarly priced ZWO ones are also absorptive. The more expensive dichroic ZWO RGB ones (not the similar priced ones for the ASI1600) seem to pass IR so will need to be used with a UV/IR cut filter as well. There have been reports of reflections and halos on bright stars with the ZWO filters (though this predominantly affects the ZWO narrow band filters). If you can afford it, like Ray I would recommend the Baader LRGB CCD Filter set at £211 pounds and have a good reputation though they are £80 more than the ZWO ones. They will last your imaging lifetime. If you buy the absorptive filters which will give satisfactory results for starting out you will invariably switch to more expensive filters in the future if you get the bug, so in the long run will cost you more. Alan
  13. I would expect the gain setting in APT to be greyed out when you connect the CCD gamera as the camera driver will not have an option to set the gain. If it's not greyed out just ignore it as it won't have any effect anyway. CMOS cameras which have gain/offset settings are only 12 bit so only have 4096 discrete levels as opposed to the 65536 levels in a 16 bit CCD camera. Trying to juggle the well depth of say 20000 -e into 4096 levels you either throw away electrons (low gain settings) or throw away even more bit depth to only 11 or 10 bits (high gain settings), or leave it at unity gain (12 bits) and accept a useable well depth of 4096. To be honest a few more clipped stars at a well depth of 4096 is not as bad as it sounds. This is all balanced with very different noise characteristics at different gain settings as well so different people have different opinions as to what the 'best' gain setting is. Vlaiv convinced me to leave my ASI1600 CMOS at unity gain as there is less faffing about. As Vlaiv said, with your CCD camera having 65536 discrete levels which is greater than the well depth there is little point in having variable gain. Here's a useful article by Craig Stark explaing gain, offset and bit depth in more detail. Alan
  14. symmetal

    repairing Synscan Hand Controller

    Good work Lishan. The original C55 is a 10uF, 16V 10% tolerance tantalum capacitor, (markings 106 16K 537). The 106E you have used is a 10uF, 25V tantalum which is why it's bigger. Similar style markings for the 16V one would be 106C I never liked using tantalum capacitors in the past (the bead variety) as they had a nasty habit of going dead short with little or no provocation. This meant the capacitor looked perfectly undamaged while components around it often went up in smoke. At least the surface mount ones while still prone to failing it seems, show themselves as being the culprits and and seem less likely to take other components out. Alan
  15. symmetal

    Class D Amplifiers\Drivers.....

    Ah! Single rail operation is OK. You'll have to stretch the 'Step' pulse to a duration long enough to step the motor or to a continuous DC output if you want the stepper motor to hold a heavy load. Class D amps will only output a DC signal if the input signal exceeds the PWM modulator's reference triangle wave, (ie. clipped) In this case it's not really a Class D amplifier any more. The main features of a Class D amplifier aren't really used to drive a stepper motor as you're only dealing with a two state signal. The 'Step Dir' signal will have to be processed too. Here's the DRV8825 data sheet and here it is with the Carrier Module used for Arduino etc. to make using them easier (£2.50 on ebay). It can drive up to a 100W stepper motor with a little heatsink. And you get micro-stepping thrown in too. For mounts and focusers you have much lower power steppers. The common high torque Nema 17 Stepper only uses about 10W. Alan
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