Actual transmission curve(HiPERCAM SDSS filter set) Toshihiko Kimura 16 September 2015 at 04:17 To: Vik Dhillon Dear Prof. Dhillon, I confirmed that the package was delivered to University of Sheffield on Monday. I will send the actual transmission curve of Sloan filter set for HiPERCAM. They are all identical with the SDSS filters for ULTRACAM and ULTRASPEC. Best regards, Toshihiko -----Original Message----- From: Toshihiko Kimura Sent: Thursday, August 27, 2015 6:52 PM To: Vik Dhillon Subject: Re: SDSS filter specifications(Spectral response) Dear Prof. Dhillon, I understand. We do *not* require you to optimise the bandpass for the f/2.47 beam of HiPERCAM - please assume that we want exactly the same as you provided us with for ULTRACAM and ULTRASPEC, i.e. "nominal cut-off wavelength in a collimated beam". We produced SDSS filters for HiPERCAM with the same as ULTRACAM and ULTRASPEC Sloan filters in a collimated beam. Each cut-on wavelength made by interference coating is based on the 20-inchi Photometric Telescope at the APO. (Please see the e-mail copy sent to you from Prof. Mamoru Doi, University of Tokyo in 2001.) Regards, Toshihiko -----Original Message----- From: Mamoru Doi Sent: Monday, July 23, 2001 10:00 PM To: vik.dhillon@shef.ac.uk Cc: t-kimura@asahi-spectra.co.jp ; Takashi Ichikawa Subject: SDSS filters Dear Dr. Vikram Dhillon, Mr.Kimura, Asahi spectra Co, asked me to explain the reason why the SDSS band response has changed from the original. The main reason is that interference filters of the 2.5-m imager changed their band responses (in g', r', and i'). We put filters into dewars, i.e. into vacuo. Then water component in the interference surfaces was removed, and refractive index changed. We didn't expect this, but we can not replace the filters. The imager is very complicated and the filters are deep inside. (Ref. "The Sloan Digital Sky Survey Photometric Camera" J.E. Gunn et al. AJ, 116, 3040 (1998) ) The filters Asahi spectra made this time have the band responses which are close to those of PT, the 20-inchi Photometric Telescope at the APO. The primary standard stars to determine the zero points of the 2.5-m photometry were observed with USNO 40-inch telescope system which has the original band responses. The PT connects the USNO 40-inch photometry and the 2.5-m phtometry, and PT system has the band responses which are almost in the "middle" of the USNO responses and the 2.5-m responses. I hope this e-mail answers your question. Sincerely, -Mamoru Mamoru Doi Institute of Astronomy School of Science Univ. of Tokyo voice +81-422-34-5084 fax. +81-422-34-5041 doi@ioa.s.u-tokyo.ac.jp -----Original Message----- From: Toshihiko Kimura Sent: Thursday, August 27, 2015 6:43 PM To: Vik Dhillon Subject: Re: SDSS filter specifications(Size, thickness, etc) Dear Prof. Dhillon, The other specifications are as follows. 1)Size 50 mm x 50 mm +0.1 mm / -0.1 mm 2)Clear aperture Min. 48 mm x 48 mm or over 3)Total physical thickness u'-band: 5.012 mm +0.18 mm / -0 mm g'-band: 5.017 mm +0.18 mm / -0 mm r'-band: 5.042 mm +0.12 mm / -0 mm i'-band: 4.912 mm +0.12 mm / -0 mm z'-band: 4.904 mm +0.025 mm / -0.025 mm 4)Parallelism < 1 arcmin 5)Transmitted wavefront error OK - I have confirmed with my optical designer that because the filters are quite close to the detector in HiPERCAM, we are not very sensitive to filter flatness, so we would not see much benefit from using the proposed monolithic SDSS r',i' filters. So please can we go ahead with the traditional SDSS construction with multiple glass layers. p-v lambda/4 per any 25 mm diameter over the clear aperture *prior to coating*. That is, we polished each substrate (e.g. KG3, UG11 and fused silica in u'-band) with p-v lambda/4 per any 25 mm diameter over the clear aperture. 6)Surface quality Scratch/dig: 60/40 7)Surface roughness Yes, I know it is sometimes (not often) shown in the RFQs from observatories. Indeed, it is quite critical for laser optics. Speaking strictly, it must be evaluated after coating. Only ion beam sputtering (IBS) technology can achieve very small roughness after coating. However, critical points in astronomical filter is definitely different from laser optics. We usually produce astronomical filters without the special consideration about surface roughness. Because again, if we try to consider, we should coat by IBS. However it is impossible to coat even 50 x 50 mm substrate uniformly by IBS due to the technical reasons. What I can say now is that our filters work well at many scientific telescopes in the world. For your reference, the roughness of substrate after polishing (i.e. prior to coating), it might be less than 10 A. Sincerely, Toshihiko From: Vik Dhillon Sent: Wednesday, August 26, 2015 4:37 PM To: Toshihiko Kimura Subject: Re: SDSS filter specifications(Prescription) Hi Toshihiko, Many thanks for the information. Please could I also ask about the other specifications: parellelism, surface roughness, etc? Regards, Vik. Vik Dhillon phone: +44 114 222 4528 Dept of Physics & Astronomy fax: +44 114 222 3555 University of Sheffield email: vik.dhillon@sheffield.ac.uk Sheffield S3 7RH, UK web: www.shef.ac.uk/physics/people/vdhillon On 26 August 2015 at 06:36, Toshihiko Kimura wrote: Dear Prof. Dhillon, I did not send the specifications yet and must do that. Each filter prescription is as follows. Our optical engineer calculated and determined the prescriptions in consideration of the given Zemax file, the clear filter for ULTRACAM, estimated thickness of epoxy-glue, polishing tolerance, or the allowable thickness of filter holder for HiPERCAM. [u'-band] KG3(2mm +0.05, -0mm) + UG11(1mm +0.05, -0mm) + fused silica(2.037mm +/-0.025mm) +: epoxy-glue [g'-band] GG400(2.042mm +/-0.025mm) + BG39(1mm +0.05, -0mm) + fused silica(2mm +0.05, -0mm) [r'-band] OG550(4.067mm +/-0.025mm) + fused silica(1mm +0.05, -0mm) [i'-band] RG695(3.937mm +/-0.025mm) + fused silica(1mm +0.05, -0mm) [z'-band] RG695(4.904mm +/-0.025mm) / monolithic substrate Sincerely, Toshihiko From: Vik Dhillon Sent: Monday, August 24, 2015 9:19 PM To: Toshihiko Kimura Subject: Re: filter specifications Hi Toshihiko, Could you also send me a prescription of the various glasses used in each filter, and their thicknesses? Many thanks, Vik. Vik Dhillon phone: +44 114 222 4528 Dept of Physics & Astronomy fax: +44 114 222 3555 University of Sheffield email: vik.dhillon@sheffield.ac.uk Sheffield S3 7RH, UK web: www.shef.ac.uk/physics/people/vdhillon On 24 August 2015 at 13:14, Vik Dhillon wrote: Hi Toshihiko, My optical designer has asked for the SDSS filter specifications (in terms of parallelism, surface imperfections, planarity, etc). I searched through my emails and I can't seem to find this information. Would you mind sending it to me? Thanks! Vik. Vik Dhillon phone: +44 114 222 4528 Dept of Physics & Astronomy fax: +44 114 222 3555 University of Sheffield email: vik.dhillon@sheffield.ac.uk Sheffield S3 7RH, UK web: www.shef.ac.uk/physics/people/vdhillon HiPERCAM SDSS filter set.xls 227K